A better one would be “there’s no proof of that, they weren’t, but don’t try and derail the conversation, stay on topic.”
Their most probable answer would be “ooooh, are you trying to deny it?”
In this case, pretend to be a noob with your views akin to theirs. Say something like “fuck no, but I need some proof to smear at my redfash friend/coworker/whatever’s face!”
And watch them try to produce it.
(Edit: Typo)
It is useful to pretend to be one of them - or at least an “initiate” in their ways.
If they shun you, then they risk looking like they’ll be driving people “to the enemy.” If they try to explain, they’ll sooner or later admit to being bullshitting.