It’s better to do one of these: (a) downvote and move on, the parent comment has a lot of hallmarks of not engaging in good faith discussion. (b) steelman the

It’s better to do one of these: (a) downvote and move on, the parent comment has a lot of hallmarks of not engaging in good faith discussion. (b) steelman their argument, improve it for them and see what conclusions are or further predictions it would indicate (c) look for evidence that confirms it first. Saying something like, “I tried to research your claim but I only found FOO, which does not include any reputable or credible sources. Meanwhile, reputable sources like BAR have said <whatever>,” is much gentler and diplomatic as well as adding new information for other participants. Other people will see the comment and realize it has no supporting argument. Any rebutting comment that only says “citation needed, your claims are extreme” isn’t helpful no matter how obviously poor quality the original comment was.