Agreed. If you are trying to convince someone else, you better have tangible evidence. I am talking about personal belief.
A personal belief does not necessarily requires evidence or at least the evidence does not need to be of a science nature. People believe in karma and the only evidence they have are the few times were karma apparently got them even with some one else, despite not being any tangible evidence that karma exists and is not reproducible on demand.
There are people here who say they respect the belief of others. Posting something about your personal belief does not automatically means you are trying to convince others. Yet, they go in there and begin to demand proof of claim. In essence, they end up doing the exact thing they claim to hate about believers. If you think a certain topic is stupid or has no evidence or foundation, simply stay out of it.
True, you are free to express your opinion. Expressing your opinion would be stating something like "I don't believe in karma because there is no evidence of it", another very different is to state "I don't believe in karma and you are an idiot for believing in fantasies and fiction". You are also entitled to think that those that believe are idiots, but if that is what you want to express, start a new thread about the stupidity of unfounded belief. Let the others continue with their lives.
Insisting on the contrary only shows an outwardly expression of your misery. I can understand where it comes from. You don't exit cults without scars, wether you like to admit it or not. But stumping on others just because of what they believe, is not going to gain you anything. Is just going to consume you for no reason whatsoever. That is off course, provided that their belief is not actually damaging you personally.