When we watch a show, we think of the characters as people. It helps eliminate the problem of people who don't think they know any gay people. Maybe you don't have a cousin or uncle who's gay, but that guy in Glee was gay, and he seemed okay right? Icons don't trivialize things in the same way, because by their nature they're viewed as different.
It's not really the gay icons as much as it is the gay banality. Having gay just exist in plain sight.
On the other hand, I recently saw a survey of Americans that tried to determine how their personal relationships with gay people affected their views of gay marriage. IIRC, around 30% responded they didn't know anyone who is gay. That said it all! (EDIT: I should be clear: My point is that there is no way 30% don't know a gay person; I doubt that's true of 1%. They are just in denial.)
I've been thinking of having contrived mechanisms exist, basically "meet a gay person" info booths.
On one hand I agree, but it's never been sufficient. There have been gay icons for a long time (probably forever); Oscar Wilde springs to mind, and Alan Turing (though I don't know if he was well-known to the public). And even with their status, they were still persecuted and ruined.