Did you just arrive from Mars to judge our discourse norms?
It's completely typical to expect someone who makes a surprising factual claim to back it up with evidence. You're talking to them because you think they might know something you don't, and be able to point to how they know it - or they might not, and them offering weak or non-existent evidence would show that.
It's completely typical to expect someone who makes a surprising factual claim to back it up with evidence. You're talking to them because you think they might know something you don't, and be able to point to how they know it - or they might not, and them offering weak or non-existent evidence would show that.