I think... most people are idiots. We all definitely can become idiots.
Celebrities, comedians or otherwise, are simply viewed usually through their work. But when you see their human side (the mistakes, the over-reactions, the sexual harassment charges etc) the image is shattered. Much more than when you hear about a pedophile neighbour, or a cousin addicted to drugs, or an uncle abusing his wife etc.
I agree with THAT.. in fact, I would restate what you said by pointing out when a comedian crosses the line between being a fictional character to being "real" they are no longer funny.
This is probably not the best example.. but it conveys the idea. If a comedian were to say.. "boy my wife is a bitch! I wish she would walk out the door and never return!" That could be quite a funny thing to say. However, if that comedian's wife really did disappear and was murdered.. that joke would then cross the line into reality and no longer be funny.
Here's another... "break a leg!" that would almost always be a funny suggestion... but if the person then DID break their leg, that would be tragic and no longer be funny (unless the person that broke their leg was crooked Hillary Clinton!)