Hahahahahaha. I can't believe people like this still exist. The chant wasn't claiming Stockdale is gay, but instead saying that wearing pink is 'gay' and therefore deserving of ridicule.
If they don't believe what they're chanting then why do it? They do it for laughs, trying to be funny by using a minority group as the victims. That isn't ok, and if you really think it's a bit of harmless banter I really feel sorry for you.
But here's the most important part: you don't get to decide on behalf of gay people whether it's offensive. The same way I don't get to decide whether certain chants are racist or not. As a white man, it's not my place to say, especially when there can be unwritten history, nuance, hidden meanings or micro aggressions behind certain words, terms or phrases that I say without thought.
Instead of dismissing people as being too easily offended, ask yourself why people might feel that way, and try to think from the minority's point of view. That way you might be able to gain a better understand of what people go through when they hear chants like that by their own fans at a football match.