I like this place. People are so nice about disagreements, here. Nice change of pace from ... most of the rest of the internet, really. So thank you for that.
That aside, I guess my whole problem with the scene is simply the fact that it was Ben doing the deed. To me, the core of Ben's character is that he's the most down-to-earth and "normal" of the FF. He's the guy that resents all the violence and weirdness he gets wrapped up in because of his condition and his situation. He's always struck me as a reactive guy, not so much proactive, so for him to travel halfway across the world to kill a guy seems pretty far out of his temperament. Plus, the sheer horror factor of watching a man's head come apart in your hand, to feel that, I just don't see Ben Grimm being able to put himself through that. He's not the hard-line soldier like the Ultimate U's Cap or Wolverine. Heck, I think I'd have even been content with having Ben let Namor out of his man-tube, there, and turning the other way while *he* did it ...
I do agree that Doom pretty much hit an "end point" here and had to be put down after all this, but it really shouldn't have been Ben Grimm to do the deed. I mean, why on earth did Nick Fury let him go? Or the rest of the Ultimates, for that matter? They were all kinda right there.