"Jesus said not to judge others!"
This is perhaps the most common excuse made, but it is ironically one of the most fallacious and the most scripturally unsound. It is an appeal to Matthew 7:1 and is in essence demanding that we not point any fingers or launch any criticisms at anyone. The problem is that anyone who quotes Matthew 7:1 completely ignores everything that comes after it.
"Judge not, that you be not judged. For with the judgment you pronounce you will be judged, and with the measure you use it will be measured to you. Why do you see the speck that is in your brother’s eye, but do not notice the log that is in your own eye? Or how can you say to your brother, 'Let me take the speck out of your eye,' when there is the log in your own eye? You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your brother’s eye." [Matt 7:1-5]The full context here is not that we should never pass any kind of judgment ever on anyone - rather, it's that we should not pass judgment upon a person when we have a greater sin of which we have yet to repent. Examples: I shouldn't pass judgment on a brother for stealing a pen from work (the speck) if earlier that day I robbed a bank (the log); I shouldn't pass judgment upon a brother struggling with lust (the speck) if I'm actively cheating on my wife (the log). Note how Christ ends the instructions: first "take the log out of your own eye," and then we will see clearly enough "to take the speck out of your brother's eye." Christ commanded the Pharisees to "judge with right judgment" (John 7:24), and this mindset is what we see being expounded upon here. Christ is not saying "Don't ever pass any kind of judgment, ever," He's saying "Don't try to help your brother with his sins when you can't even see your own sins."
The fact is, scripture gives clear commands in regards to rebuking. Christ organized a system by which you could rebuke a brother in the church (Matt 18:15-20). The repentant thief on the cross rebuked the blaspheming one (Luke 23:40). Paul rebuked Peter (Gal 2:11-14). Paul likewise commanded believers to rebuke (1 Tim 5:20; 2 Tim 4:2; Titus 1:13, 2:15, 3:10-11), and even said that was one of the duties of church leaders (Titus 1:9).
Now, are there wrong ways to rebuke or reprove? Of course, but we shouldn't jump to extreme examples to dismiss rebuking and reproving altogether. We also should not jump to Matthew 7:1 as an answer to every kind of rebuking out there. That not only shows ignorance in regards to what Matthew 7:1 says, but what scripture says as a whole.
"They've blessed a lot of people."
This is essentially an argumentum ad populum - that is, a person is a good teacher/minister/pastor/prophet if they have a large following, congregation, or a lot of people have supposedly been saved by them. It's also a pragmatic fallacy in that it essentially argues, "Who cares if the person commits error so long as someone gets saved?" This is most often used in defense of those with megachurches, large ministries, or generally those with a huge following.
The problem is that sheer numbers does not equal right. Scripture makes it clear that true believers are often in the minority when compared to the number of false believers or unbelievers (Gen 6:5-8; 1 Ki 19:18; Isa 1:9; Rom 11:5). Also, if anyone is saved, it is not because of the teacher, but because of the grace of God. No one deserves any credit for the salvation of a person but God and God alone. Soli Deo Gloria.
I might add that this line of reasoning introduces a kind of pragmatism - that is, how cares about the teachings or the methods so long as numbers are growing? This forsakes sound biblical doctrine, which by its nature offends (1 Cor 1:18), to make room for methods and teachings that attract larger numbers.
"Don't criticize it until you've experienced it!"
This is the classic "don't knock it 'til you've tried it" fallacy, and is commonly used in regards to Hyper-Charismatic or Neo-Pentecostal heresies which place a heavy emphasis on experiential worship. The point of this argument is to discredit the other side by arguing that they have no right to make any declaration until they have experienced the very thing they're criticizing.
Of course, this entire argument is a red herring that completely jumps from the argument, ignores everything said by the other person, and makes a mold declaration that has to be met. It places the weight of evidence upon the other person and demands they defend their position when there is no need. It's likewise an overarching argument that can be used to defend anything. Permit me to give one example:
Person A: "Boy, I sure enjoy sniffing glue!"
Person B: "Dude, you realize that will kill your brain cells and lead to greater drug use, right?"
Person A: "DON'T CRITICIZE IT UNTIL YOU'VE EXPERIENCED IT!"
Do we now see how irrational this kind of argumentation is? Person A completely ignored everything Person B had said and simply jumped to an emotional argument. A person does not have to experience something to tell whether it is right or wrong.
"They're a nice person."
I've actually had people use this excuse. It's as if we should throw out bad teachings, bad ministry practices, or immoral character simply on the basis that, upon being met, the person was overall agreeable. Are we supposed to presume a person holding heretical views will automatically have bad personal traits, and likewise presumes that a good personality covers heretical views? This is a false equation: that a person is "nice" does not mean they will are orthodox; likewise, that a person is "mean" does not mean they are also heretical. Some of the worst heretics in history were said by their contemporaries to have been nice or had some redeeming qualities - that does not negate their error.
"Who cares as long as they talk about Jesus?"
This is perhaps the worst argument to make. Our Blessed Lord taught:
"On that day many will say to me, 'Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?' And then will I declare to them, 'I never knew you; depart from me, you workers of lawlessness.'" [Matt 7:22-23]It is not enough to have the name "Jesus" in your statement of faith. It is not enough to have the name "Jesus" in your ministry. It is not enough to simply claim you believe in a man named "Jesus." In this day and age when statements of faith are often put up simply as a front to appease critics, we must go deeper and understand what a person really means when they call themselves Christian or refer to a belief in Jesus. Faith has to also display regeneration, and it has to show a love for God's word and an adherence to what God calls the truth. If the person shows none of this, then they do not have Christ, and do not deserve to mention His name even in passing.
"You're being mean!"
This is oftentimes the last card played by the individual supporting the false teacher. Granted, there are wrong ways to approach error (see my post here), but generally this is said when there is nothing left for the person to say, and in the spirit of true emotionalism will attempt to simply accuse the other person of being a jerk.
Aside from being emotional, it is also a red herring. Let us say, for the sake of discussion, that the person really is mean. Does that automatically negate everything they say? If it's a sunny day, and a mean person says it's sunny in a mean way, does that mean it's no longer sunny? Of course not. In like manner, truth does not stop being truth simply because of the delivery.
"You don't know this person personally!"
The gist here is, since we don't know the person on personal terms, we shouldn't comment on their teachings or motives, and to do so is premature.
The problem is that you don't have to know every ounce of a person to know something they've done is wrong. If a man cheats on his wife and is caught red-handed, do I have to know them personally before I can say they're guilty of adultery? If a man is proven a murderer by the law and sent to jail, do I have to know them personally before I can say they're a murderer, or guilty of murder? The most obvious to all these things is: no. The requirement to know the person on a personal level is a condition added on to avoid responding to the situation. If a person teaches doctrine contrary to or removed from scripture, then they are teaching falsely and hence are false teachers. We don't need to have a few beers with them before we can say this.
The apostle Paul, speaking to the Ephesian elders, said:
Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God, which he obtained with his own blood. I know that after my departure fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them. [Acts 20:28-30]Paul does not say: "After my departure fierce wolves will come in among you, not sparing the flock; but make sure you know them personally and if you do, then you'll know if they're wolves or not." On the contrary, he says that they will know them because they will be "men speaking twisted things." If the Ephesian elders encountered men speaking twisting things, how well they knew them personally was a moot point - they were wolves. Scripture always distinguishes false prophets by their teachings and not their personality.
The worst thing we can do is forgo sound doctrine for the sake of superficial peace. As the apostle Paul wrote:
But I am afraid that as the serpent deceived Eve by his cunning, your thoughts will be led astray from a sincere and pure devotion to Christ. For if someone comes and proclaims another Jesus than the one we proclaimed, or if you receive a different spirit from the one you received, or if you accept a different gospel from the one you accepted, you put up with it readily enough. [2 Corinthians 11:3-4]