No.

I'm saying asking for sources as a way to express "I don't believe you" is a bad thing.

First of all for the reason I've just given.

But second, because it's passive-aggressive, disguised as interest in discussion, yet so transparent.

I'd generally prefer discussion on Hacker News was kept civil. If the parent had a reputable source for their assertion, I'd be interesting to see it. A lack of a source is also interesting.

Either way, asking for a source is better than just saying 'I don't believe you'.