The way I see it, the only person who can really judge a person is that person themself. Corollary: don't judge others without robust evidence, and don't accept the judgement of others without robust evidence.

As for how one judges oneself, well that's one purpose of philosophy - to help one reflect on oneself.

It's really quite easy to separate the hypothetical from the real: just keep asking "How do you know that?" or "Why?". In my experience, it never takes more than 3 or 4 iterations to spot the hole in the evidence.

Sometimes, the holes are inevitable and more a part of the human condition; but lots of times, it all reduces to bald assertions, cherry picking, confirmation bias, and all the other cognitive biases and logical fallacies.