My first argument, just to see who's paying attention (my guess: no one).
Media portrayal of non-hetero-normative relationships is at best weak, and at worst, damaging to the groups represented. While there is more nuance to these portrayals, it's interesting to look at some of the more damning evidence.
Will and Grace is a fairly recent example. Will is the straight man to Jack's flamboyant counterpart. Jack represents the stereotypes of the feminine homosexual, speaking in a higher octave than most men, focusing on superficiality in most things he says, and berating Will for not being as attractive as he should be.
To his token, Will is the more straight-laced, the not immediately noticeable homosexual who's only vice is exhibited in his friendship with Jack - that Will, if anything, isn't gay enough.
But why focus only on Will and Grace? There are, after all, other instances of homosexuals in the media, and what positive examples they are:
Queer As Folk - while this television show does tackle some serious issues, the primary location is a gay dance club where drug deals and sex take place in the back rooms. Many of the episodes metonymize gay life into a series of one night stands interspersed with crystal methamphetamine use.

The L Word - more than Queer as Folk, sex is what sells this show.

Tobi, from Family Guy, a show known for pushing the envelope of what can and cannot be said. Other instances of popular homosexual characters include Herbert the pedophile and Stewie Griffin.
The issue with media portrayal of characters is that, in many ways, the media informs us of how we should act. Television, especially in a country where so much emphasis is put onto television, provides cues for social behavior. Who didn't learn a lot about interpersonal relationships and communication from Friends? So my question then is where are the cues for positive homosexual social behavior? Where do homosexuals learn these cues from?
Another way to think about it is this: we're all taught that men date women. So even in elementary school most of you can remember having little "girlfriends" or "boyfriends" or getting your first kiss at 11 or 12. You probably experienced going on dates after, or sometimes before, you learned how to drive, and of course everyone knows how important prom was.
What happens to a group that isn't represented by those "men-date-women" stereotypes? What happens to a group that gets that chunk of their life, all of those formative events, withheld until they're 18 or 19 or even in their 20s (since college is the classic coming out time)? How are homosexuals supposed to act without any positive media role models, or do you think some of these scenarios do represent positive portrayals or can you think of other positive scenarios?
Finally, consider what happens when you separate a group of people based entirely on their sexual orientation; won't that group be more sexual by default?
What are your thoughts?