Being kind to them is completely wasted effort.
Replying to them is also wasted effort as they won't be persuaded.
However leaving bullshit unchallenged might make trusting bystanders believe that this is actually the truth.
one side of this debate is very much NOT acting in good faith because they rely on the status quo being maintained to continue what they are doing
I still suck at this in practice but I'm sure of it in theory!
(I'm working on a longer reply to you at >>39158911 , but I can't resist replying here too because I feel like I figured this one out after 15+ years of frustration.)