I guess most people here aren't moral relativists? Most people, including myself, think that homophobia is imprinted, awkward, backwards, reactionary, delusional, unfair, exclusionary, bad for society as a whole and terrible for the safety or peace of mind for individuals affected. I'm not sure that makes homophobia wrong, and I think that terminology is...unhelpful. "Right" and "wrong" are absolutist claims, and thus extremely easy to tear down (or slip down the slope into tunnel vision), especially by people who think of everything in terms of absolutes.
TL; DR!
Carpe diem!

I'm a moral relativist in some places, not so much in others. I can see what you mean about absolutist terms, and I guess I agree, but I don't really know how else to describe my reaction and my viewpoint, so I don't know what words might be better.
I don't mean to sound combative, but I can't just carpe diem when homophobia leads to violence. And the thing is, I never know when that might be. I've had people follow me into parking lots with the intent to beat the snot out of me; at the time, these people were total strangers. I later found out that they were friends of friends - people that I thought were "on my side", so to speak (I lived in a small town at the time, so the coincidence wasn't that shocking). For LGBTQ people, that's often a pretty real fear. Sure, in a lot of places, it's rare now, and you don't have to worry so much. But in others, it's part of life. Someone might try to hurt you for who you are. Of course, that's a pretty extreme example. But for the majority of my life, it's been my reality. I know you were talking about the whole slippery-slope thing, and that's kind of my view on it. Most people aren't going to do anything to me, except maybe throw out some rude words. But there's always going to be people who will hate me for who I am, and how do I tell someone who's just a bigot, and someone who's going to use that bigotry? There's no litmus test, unfortunately. It would be super-convenient!
I think alot of people love to slap on labels.
I worked with a couple of gay guys and got along fine with them!
One was a Liberache type and I was constantly joking with him (since he insisted on being in the closet I would ask him for pointers on cruising the babes - they all loved him! It was great fun for all of us ESPECIALLY him - he genuinely laughed at the things I would say.)
The other one I asked alot about the gay lifestyle because I was as interested as I would be in another culture.
Like one question: does it ever bore you or get annoying to have sex so often?
Turns out it's quite satisfying apparently.
Well, great for him! As for me, I'm not interested in being any part gay, and so I'm sorry - when people try the stunt of "well you haven't TRIED it" I'll tell them they're frikkin idiots and to fuck off. What makes me a homophobe simply because I don't want to be any closer to a gay guy than arm's length? Why should I have to have no problem with a gay in my personal space to NOT be a homophobe? Why aren't some of them HETEROphobes for insisting that there's something wrong with straight men?
I think alot of people today are very fast to slap a label on something without even thinking about it, simply because they're raised to do so.
What makes that a homophobic view is that the language you've used suggests that you have a special standard for gay men. You're presumably okay with people who
aren't gay men in your person space. Generally, when we say we want to stay "an arm's length" away (or other units of measurement, like "wouldn't touch it with a ten-foot pole"), we're doing that out of protection for ourselves, disgust, or fear. If you can't catch being gay, then why is it a problem? To say you don't want men hitting on you isn't necessarily homophobic, because you're not attracted to them - it's not a whole lot different than saying you don't want women you're not attracted to hitting on you. It's the special standard that does it.
If gay men are insisting that something's wrong with straight men, yes, that's a crappy thing to do. If they don't want to be any closer than an arm's length away, then I suppose you could use "heterophobe" - again, it would have to be the special standard applied to only straight people. But the sheer numbers of people suggest that it's not very likely that a gay person could really enforce such a thing, as the majority of people in the world aren't gay. I've never personally known a gay person who thinks that straight people are "wrong", but of course, I don't know all the gay people in the world, so it's totally possible (nay, probable!) that people like that exist. And they're being crappy for it. But that's not really the issue at hand. The issue is talking about how assumptions and homophobia are enacted, and why it bothers people. I'm guessing that the forum members who are reacting strongly are close to GLBTQ people, or are GLBTQ themselves. It tends to hit a little closer to home, and there's a certain amount of emotional engagement that's really hard to explain to someone who isn't affected like you are. If you're a straight man, you've never experienced the fear that comes from a gay-bashing. I can't explain it to you - it's not the same as getting beaten up on the playground. And the connections that are made between a casually homophobic comment and the attitudes that affect our lives negatively can seem like exaggerations or overreactions to people who aren't in the same position. When I hear someone around me make a homophobic comment, everything changes for me - is this person dangerous? Do they know about me? How deep does this go, and how am I going to handle being around a person like this? It's never an easy thing.
But my goodness, this is getting TL;DR!
Short version: GLBTQ people are probably going to see a homophobic comment in a very, very different light than someone who isn't GLBTQ!