You’ve got a variety of responses here.
If Obvious Troll Is Trolling, your answer is not going to educate them, the question is likely going to be deleted anyway, and your answer will become inaccessible unless you archive it off to a blog. As many have said, Konstantinos Konstantinides’ answer most succinctly.
If you write a good answer anyway, i.e. answer it appropriately: don’t do it for the OP, as Tong Hui Kang’s answer argues. Do it to spread good information. And do it if you think it is really important to spread that information, because the risk that the question is going to be deleted anyway is pretty strong.
Don’t do it to give a withering witty reply back. Not unless it’s Oscar Wilde God Level funny. Countersnark gets boring quickly.
Don’t do it to virtue signal. I don’t care if the term has been appropriated by the Cultural Right, it points to a real phenomenon, there’s way too much of it on Quora, and it is boring. And not particularly informative.
Don’t do it to flame them right back to oblivion. The way BNBR works, you’ll be the one ending up in oblivion.
And lastly and most difficult of all: Do not assume by default that everyone who disagrees with your worldview is an Obvious Troll Trolling. Stating that assumption in an answer is, in fact, a BNBR offence. (I’m sure Jennifer Edeburn has the reference for that somewhere.) Hanlon’s razor applies to Quora questions, just as it does to Quora UX.