Part of my own reasons for contributing to a site like this are to increase the signal-to-noise ratio, i.e. to provide a source of additional correct information. However, I despair of ever actually changing anyone's opinion or belief, about anything.
It seems to me that people simply cannot be influenced by exposure to better arguments or information. Whether this is due to cognitive bias, or arrogance, or the fact that admitting you're wrong is too damaging to your self-worth, or whatever. If you have a better argument than someone else, all you're likely to do is alienate them.
Personal example: I've engaged in a number of lengthy debates with very smart lady friend with a university-level science degree who believes wholeheartedly in the virtues of homeopathy. I do not, and have spent considerable effort trying to convince her otherwise (the fact that she's a close friend mean that I can be fairly forthright while staying civil). No luck - she knows what she know, facts be damned.
Are we all just adding to the noise?