It was a reasonable request. You appear to be upset about being asked for supporting links, despite having made the same request yourself. I genuinely don't understand that. I'm concerned that we're drifting too far away from the orignal topic though, so there may be limited scope to explore this aspect of things here.
A: Claim X.
B: Can you support X? Claim not X.
C: Can you support not X. You should provide support for not X before asking for support of X.
Is it really reasonable to call out B for not providing support and not call out A for the same? B was the first to ask for sources, but A made the claim without sources. It also seems like if B only made the claim not X and didn't ask for sources, they would have been less likely to be called out themself.
So is asking people who ask for sources to provide sources really reasonable when we don't make the same request of people who are making claims without any sources? It seems to give a first move advantage and thus wouldn't be reasonable.
Sorry, I've only just seen this. Your breakdown doesn't reflect what happened here. You would be correct if all B had said was "Support X".
What we saw above was:
A: Claim X
B: Support X, I've observed Y.
C: Support Y too, please.
In this particular case, Y was arguably the inverse of X but it was nevertheless described as having been observed many times, but without any sources.
