After checking out some people's reactions and realizing that we as viewers are purposefully being led to believe that MIB's intention with that bomb was to kill everyone on the sub, I respectfully propose that he was only trying to kill Jack. MIB has made it clear in the past that people who are unwilling to dismiss the idea that they are doing the right thing by following Jacob, are going to have to die. He asked Jack a few times to reconsider, and when it was clear that he wouldn't, he set him up for the kill.
My evidence to support the fact that he didn't intend to kill everyone on the sub is as follows:
1. His original plan was to get on the sub with everyone... Why nuke it? 2. He called out to Sawyer in a distressed manner when he was locking him out. 3. He stopped Claire from trying to get on the sub.
I also find the closing scene to be interesting. We're led to believe that MIB is going off on a mission to kill the remaining sub survivors, but I think his intention is still to only kill Jack.
P.S. This is my first activity other than daily reading of blogs from work, which I've been doing for quite some time. I saw that there was a lot of talk about people posting spoilers and suggestions from the community about banning all newbs, or turning off their ability to post for xx days, so I just wanted to get this idea out there in case any of that went into effect.
P.P.S. The "next time on LOST" really gave me hope that my original theory about MIB not being the "bad guy". HOPE!