...did you just skip the first part where I literally preface my argument with this line?

> Assume they're being 100% honest that they genuinely believe nobody disagrees with their statement.

That's the core assumption. It's meant to give them the complete benefit of the doubt, and show that doing so means their argument is either ignorant or their perspective that opponents aren't people.

Obviously they're being dishonest little shits, but calling that out point-blank is hostile and results in blind dismissal of the toxicity of their position. Asking someone to complete the thought experiment ("They're behaving honestly, therefore...") is the entire exercise.