The genre is a fantasy outlet for women. In movies like "The Change-Up," the women who see this (who the studio strives to get in the theater door) want to believe that good, honest men won't use a free pass to act on his wild manly impulses, that love or something of the sort is enough to keep them reigned in. And speaking of, what about that "Hall Pass" film. Didn't see it, but my understanding is that these dudes don't even end up having any flings, even then they are sanctioned by their wives!
If you've ever heard of the theories that Hollywood gave us films of decadence during the Depression to offer an escape from the misery of real life, it's the same principle. Every other week there is another noteworthy man cheating, whether it be with prostitutes, rent boys, or every lady they could get their hands on, the news is a constant parade of unfaithful men. For women, it brings a lot of anxiety, I'm hearing it and seeing it, some wanting to talk about it and others wanting to ignore it, but it's palpable. So if a lady today wants to escape the anxiety of her real world, she goes to see a film where the man never cheats, he never gives in to his sexual impulses, and this is possible because of a wonderful, sassy, smart, funny, successful, and beautiful woman. It's actually kinda sick - if a woman can be that perfect, put-together picture of romcom success, she will land the man who will love her faithfully forever.
I think Stewart is giving the audience more credit, not less, and pointing out that these people *are* smart enough to not wish for the death of innocent people. It's because these people are on a higher ground - intellectually, morally, ethically - that it shocks to have them applaud. These are your neighbors, who you would never think of as violent or angry or aggressive, who deep down, in a place beyond reason, have a strong gut reaction toward capital punishment. I don't know, I honestly can't believe it was viewed as him calling the audience stupid; perhaps it is too subtle a difference, but accusing someone of using their gut over their brain, especially when those brains seem to be functioning quite well, isn't trying to say "turns out these seemingly smart people are dumb" but rather trying to say "these seemingly smart people can still be swayed by the oftentimes irrational but obviously powerful gut."
And as for the lawnmower/blind side/raisins description, describes most people I know from home (N. Georgia). It's actually quite a nice way of showing how they are different from, say, urban dwellers *without* calling them outright stupid.