Defaulting the font is the only way I have yet found to deal with the fact that site users are using a vast variety of screen resolutions. I can't set the font size without making it huge on some screens and tiny on others. At least with defaults most people can change the setting and have it stick. On top of that, unfortunately, the most readable font family, Verdana, displays with wild variations in size across platforms, which I think is weird as all get-out but there it is. Even a family of sans-serif resulted in a number of people complaining that they'd gotten Verdana and it was too big.

So the only real option I'm left with is either default or something universal like Arial, which is uniformly small on pretty much all browsers. And when I started out with that, in the beta-testing process, people howled about how tiny and unreadable it was and asked for a different font.

I would be willing to set it to Arial if that's really, really what the majority of users want, supposing that the majority of users can ever be bothered to actually respond to "do you want" posts or polls beforehand, which evidence suggests is not the case. But, frankly, at this point, only if someone else is willing to explain the choice to everyone who will, without fail, come and complain about how difficult it makes things.