On the one hand I agree with you, on the other hand I think this is highly idealistic:
Most people would have a hard time debating a flat-earther since it's their hobby and they master all the talking points whereas you spent maximum one hour even thinking about it in the last 10 years. They will get you in a dark forest of details you don't know how to navigate and win the argument.
I am so sorry for the one in a million crackpot-sounding genius that will get hurt in the process but social shunning is just so so much more effective. No wonder the crackpots and grifters are back and running the show nowadays
I think a better approach is to ask people who have contrarian/non-consensual opinions to show that they know that they are crackpots out and to distance themselves from them:
"I know some people come up with conspiracy theories that says climate is a hoax designed to control populations because they don't want to change anything in their way of life but that's not what I am. I just care about the science and I think I found a real flaw in the leading explanation of climate change. I'd love for someone with knowledge about to discuss it with me to see if they took X into account" etc.
This above is what I expect but if you quack like a quack, you're probably a quack and you'll get the social shunning treatment