Ok, here's my view on this.
Hamilton cut the final chicane and therefore needed to give the position back to Kimi. He did this however, in a way which let him past, but still gave Lewis a big chance of passing Kimi into the next corner. He should have backed out and tried to pass somewhere else, and then he wouldn't have got the penalty.
Sometimes you just need to think about something before you make a decision. Hamilton obviously thought he was doing the right thing by letting Kimi back through, but then immediately attacked him at the next corner. to be honest I wasn't at all suprised by the decision after the race, I could have seen it coming.