It's funny, because I really hate photographs of myself and couldn't figure out why for a long time.
For a while, I thought it was because I hated the angle or the flash or the depth of field that the taker had used. I also liked the self-portraits that I'd taken of myself, which I felt captured me at my most flattering.
At some point, I realized what the truth was: the photographs that others took reflected how they saw me, but the photographs I took reflected how I saw myself, and the disconnect was in between the two. The photos I took of myself reflected my vision of myself, who I saw in the mirror every morning. By contrast, the photos other people took of me reflected the multitude of unflattering and ungraceful angles that life happens to give us. No one looks good from every angle, and we all have our "good side," which we like to tout and display and capture. The problem is that other people don't always realize this, or (even if they do) bother to capture it.
I look cute when I do it myself.
A site with a community is pretty much the same way. I think every community-driven site has an audience it associates with itself. The "trouble" comes when you realize that your actual audience is overwhelmingly not who you think they are.
A good example of this is Twitter. Twitter has a really interesting, intelligent userbase, in certain pockets. There's good, revolutionary political discussion happening in many corners of their service.
However, even a cursory glance at what's trending worldwide reveals who Twitter's actual audience is: a huge portion is urban youth, largely black and Latino. There's also a giant youth fan coalition on Twitter. Apparently, adolescents (also known as "tweens" and young teens) have the perfect attention span for and internet access allowances for Twitter.
Currently trending worldwide: soccer, One Direction love, something inappropriate, Jonas Brothers, etc.
Twitter's embracing or disavowal of this audience is totally secondary; they're there, and people are going highlight and display these audiences regardless of what Twitter wants press coverage to look like. It's the tech news equivalent of having photographs taken by paparazzi as you stumble out of that club at 2am, the flash catching you as you're mid-blink. It makes you look awful and misrepresents you an amazing amount, even if that's how you look to your friends 15% of the time.
Another good example of an audience not necessarily being who you thought they'd be is Tumblr. Tumblr is amazing! Lots of tech startup-y people short-form blogging about stuff they love. Designers putting up samples and inspirational paint chips! But you know who else is on Tumblr? Fandom! Lots and lots of screaming, excitable fans posting gif after gif of Justin Bieber or Ron Swanson or from Adventure Time.
The thing is, Justin might be dancing like this until the universe dies of heat death...
Seriously, he will be doing this until the end of time.
But these periphery-now-majority audiences aren't a bad thing. At the end of the day, Justin Bieber fans might also be politically active and, one day, become community and world leaders in their own right. They'll add value, and likely will add value to your service first, before they move on.
Think about all the screaming NKOTB fans who painstakingly cut out pictures of Jordan Knight out of issues of Seventeen and Tiger Beat. Those people are (probably) well-adjusted human beings now, the days of pink leopard print tapered-leg pants and Doc Martens well behind them. They're volunteers, senators, teachers, civil servants, and more.
My point is, this amazing collection of people makes your product/service way more valuable. Having an audience that doesn't resemble your self-image isn't inherently a bad thing. Surprising? Certainly. A little shocking? Very possible! Harmful? Unlikely; every single person using your site increases your site's reach by nearly an order of magnitude.
That said, it's your responsibility to, as with any person, employ a little creative Photoshop. I'm not saying you should relegate these people to a ghetto (the way Amazon did with GLBT and erotica writers) but fashion your product to allow discrete audiences discrete spaces. Twitter offers me trends it thinks are relevant to me based on my preferences. Tumblr makes it easy for me to stumble upon the content (and gifs, let's be real) that I care about. Filter, carve out niches, and allow these little garden plots of communities to grow; eventually, you'll find that they want more, and you'll be able to say, "Hey, I have that, too."
Take Stack Exchange. We see ourselves as a site mostly for programmers. And, to a degree, that's true. We've got lots of topics covered that are (mostly) relevant to programmer-only audiences. But we're seeing that change. We're gaining ground in the gaming community, and we're seeing more scientists, artists and graphic designers, researchers, and even librarians! Our audience is evolving. While sometimes we get called out for not knowing who we're serving, at the end of the day we do our best (as Community Managers, developers, marketing, sales, whomever) to give each of these groups the tools and toys they need to flourish.
This was adapted from an impromptu talk I gave to a bunch of people from Business Insider when they came to visit a while ago.