"They don't even have to have any actual evidence for the claim they are making at the time. All that is required is that you challenge them."
Pretty much the norm now in western culture. People have become such idiots, the culture hardly seems to merit saving.
"If you challenge vaccines in any way you likely will get called an anti-vaxxer. "
Shoot, around here it's the opposite. Say anything good about vaccines, or note the eradication of certain diseases thanks to them, and you are some sort of big government vaccine shill.
I think anti-vaxx is the most rabid ideology around here, probably followed by anti-tax/government.