I agree completely, so I couldn't answer this. I personally love all the main characters but think they'd all be annoying in their own way in real life. And, I definitely feel the same way about the audience's selective grace. They cut characters like Gloria, Haley and especially Jay so much slack for nearly everything, but take other characters' (like Cam and Alex) flaws and bad moments incredibly seriously.

Some of their criticism definitely makes sense. Cam and Mitchell do always lie to each other, but then again... so do the other two couples. That's a fairly common formula for sitcoms. In general, I think the show does a good job of exhibiting unhealthy patterns of behavior in relationships but also portraying that couples can work past it. And besides, like you said, most of the comedy is derived from the complicated relationships within and among the family.

Cam faking a divorce for attention and affection was messed up. But it was resolved by the end of the episode and the other two couples also hurt each other inadvertently and sometimes knowingly. I've seen people call Cam emotionally abusive, but Jay actually neglected his children and hurt Mitchell. He also mocked Gloria's culture repeatedly through the show and rarely gets called out for it, on the show or by the audience.