Comedies tend to mock everything, it is not isolated to sexuality. Personally I think that and the general unfunniness of the writing is why they all fail in the first or second season
I've read the Happy Endings thread here extensively and the main complain, way before the cancellation was announced, was the frantic way everyone acts. The characters themselves behave as if they are on speed and so do the storylines. Everything is over hyped to the point where you just can't suspend believe anymore
The portrayal of gays, race and all other social issues suffer from the same fate IMO
Well there are ways how these issues can be portrayed. Mocking sexuality, ethnicity etc - is hardly classy or funny. And I do believe comedians and writers have moral responsibility towards the viewers in handling these. Well obviously they have the "right" to show whatever crap they want to, but that's besides the point. For instance, if you watch British comedies - Alan partridge is a good example - he's homophobic, racist, etc. - a total d-bag - but he's the one being laughed at. That's the key difference IMO.
As for Modern Family - my main complaint is that, personally, I think it ruined a great opportunity for a much healthier portrayal of gay couple - I just can't get past it, that's all. It's not as if their portrayal is offensive or anything, FYI.