A) "All gay people are paedophiles" is clearly offensive nonsense; and so is "All paedophiles are gay".

B) "No gay people are paedophiles" and "No paedophiles are gay" are clearly, regrettably, false.

The trouble is that attempts to challenge the nonsensical propositions in A can be confused with defending the equally nonsensical propositions in B, and the other way round.

And if we think our opponent is saying something as offensive as "All gay people are paedophiles" or as dangerously misleading as "No paedophiles are gay", it is no wonder if tempers get raised.

(Replace "gay" by "straight" in this post if you prefer.)