I agree that it shouldn't have been Rondo who stepped up, but someone had to. I can think of several occasions over the years where a player took a hard foul and none of his teammates did anything about it. One case that comes readily to mind is when Pierce dunked on Bosh in Toronto a few years back, and Bosh took one in the boys. The recurring comments centered around how no one "stood up for" Bosh, and what a sad commentary that was on team chemistry and how little respect teammates had for Bosh.
Right or wrong, Rondo took it upon himself to demonstrate what should be done. In a perfect world, it would have been a role player, and not the star of the team. But as a leader, it's possible Rondo felt the need to demonstrate the sort of response that was required, perhaps because he had no reason to believe any of his teammates would do it.
I don't want the best player on the team doing the fighting - I want him on playing, not suspended. But I think an argument can be made that Rondo, especially in light of how the C's were playing that night, wouldn't have had any reason to suspect that anyone else was going to do it. I sure can't think of anyone else on the team who was gonna get in Humphries' face.
For the record, though, to me it looked like Rondo shoved Humphries, and was moving to go get KG. Humphries held on to Rondo and the shoving escalated because he didn't let go. I can't see how Rondo gets stripped of his Jersey unless Humphries is engaged in the wrestling match as well. Rondo instigated, but Humphries was certainly a participant and not an innocent victim. If he shares culpability for the fight, he should share the burden of the punishment. He got neither fine nor suspension.