I’m saddened but not surprised that so many people on this site don’t get Modern Family.
Why would someone as gorgeous as Sofia Vagara marry someone like Ed O’Neill’s character? Perhaps because she’s a single mother who has had her fill of men who can’t see past her looks and finds a fairly wealthy man who is smart enough to have created a successful business, is gruff but basically kind, and treats her son as his own, even though their tastes and interests are completely opposite, to be just what she needs.
It’s pretty apparent that the O’Neill character is very uncomfortable with his son’s homosexuality. Given the fact that he’s far from reticent, it’s pretty unlikely that he wouldn’t have made that fact known to his son. But this is a sitcom, not a morality play, and a discussion like that on screen would be out of place. So he continues to love his son (that whole “hate-the-sin-love-the-sinner” thing) and does the best he can to maintain a relationship.
I don’t think it’s unintentional that the gay couple who strive so hard to be perfectly correct are creating a bratty child. I think it’s an intentional poke at the downside of political correctness.
The rest of the characters are often shallow, vain, selfish, jealous - just like most of the people in my family. (Not I, of course.

). But they do generally try to do the right thing in the end, and, as much as they squabble, they love and support each other and deal the best they can with their family as it is today.
Frankly, I think there are many shows that are far worse than MF.