Answering, "You can't let one bad person define a religion!!"

Actually you can define a religion by bad people if there are enough of them.  But even that is not simple.  Those who use the argument really mean that they are going to ignore the harm done in order to make the religion look clean and immaculate.

With evil people and religious tyrants both in the religious political system or the religion itself (eg Pope Innocent III) claiming to be Christian (or whatever) and a supporter of Christianity (or whatever) you may say that one bad or mad man doesn’t define a religion. He does if labels are just words and can mean anything! To stick a label on yourself and another person just because religious ceremonies of initiation were performed and when the label is nominal is to accept that person with their actions.  It is going out of your way to connect with them so that shows some measure of approval for their evil.  It may be a little but a little is enough to make you worthy of condemnation.

And one person defines a religion if the religion put him in power or if he would not be in power unless the religion existed. Indeed in that case it is the bad user of the label you should think about not the good ones. Why? For stopping evil is a good work and the best good work. Then you can get on with active good works. Doing good while doing nothing about evil shows the good is being done for your glory and not for the sake of goodness. You are not a genuine person.

Why can’t his definition be as good as yours or not better? If a label means whatever you want it to mean then you have to agree with his labelling of Christianity as bad. If Jesus is real and is alive and is evil then it is up to him to decide who has the label for real or deserves it better. That could be Hitler!

If Jesus was a fake and was sowing seeds of violence and sectarianism without making it obvious or even if he was blatantly evil then you can define the Christian religion by him.  A bad founder defines the religion.  The good followers need to see that they are only making good difficult for themselves by being good in spite of the poison that drips on them from him.

You need to see the evil done by others in your species as a sign of what evil is possible for the human species of which you are a part. You need to see the evil done by others in your group as a sign of what evil is possible for the human species when it organises into a group like the one of which you are a part. So the evil of others is in some way your problem and at the very least you must take action against that evil. Refusing to take any responsibility or accept that you are in some way linked to the evil and it to you is a denial of what you are. It is paradoxically a form of objectifying. You deny what you are in order to glorify a group or religion or whatever. Religion seeks glory more than anything else does so it is the worst offender especially as it worries more about labelling than anything else. Without sticking nominal labels on people as much as it can, religion would only be the fifth of the size it is. The religion by getting you to become an object in that way is not respecting you and at least you know why religions tend to persecute their own as much as outsiders. Objectification is a form of violence and gives more power to violence.