I can see why they went with Iceman. In the comics I can't think of any serious relationships he was in (though my knowledge of his history is limited) and in the first X-Men movie it was heavily implied he was gay although it was all contexted as his being a mutant, switch the "mutant" for "gay" and you've got the same story.
The scene with Wolverine in the kitchen, the way his mother says "can't you just stop being a mutant," etc all were fairly obvious allegories for being homosexual.
Was it necessary? I think it was although obviously it is going to rub some people the wrong way, it also was not nearly as heavy handed or clumsy as some previous "outings" have been. Creating a new hero who happens to be gay is not a solution because it looks even more like pandering than retroactively altering a superhero's past, which is incidently so common I don't think I need to list the examples of it to make my point.