In the case of Milo, this is a fair pre-judgement. Are we expected to ignore a person's entire corpus of work and treat them as an untouched field of snow every time they present themselves? We're to "rehash" their position every time they speak? That seems silly.
People like Milo form their careers on rage-bait. Shouting him down is the same as simply banning a troll or banning flame-bait on forums.
For the others, for the most part it's the same - reactionary speakers, especially in the USA, are mostly uninterested in good faith debate. They leverage rhetorical fallacy and outright disinformation to muddy the waters. See: the Trump election conspiracies, the antivax movement, the rewriting of the cultural history of gender fluidity to attack trans people's existence, etc etc etc.