I guess that's how some people justify endless Internet arguments with creationists, conspiracy theorists, and what have you. You're never ever going to convince your opponent, but with luck you might be able to convince some of the bystanders.

However, I agree that as you said, to be effective you'd likely have to reach out to the bystanders directly, and with an approach rather different from the decidedly unkind manner that those discussions are typically conducted.