I think to some degree all of us have some munchkin or power gamer in us. For most, though, it's so mild that we refer to it as character optimization. We roleplay a bit, we optimize stats when we spend xp and generally respect that we're not the only people playing the game. There are others at the table. It seems like people misue the terms munchkin and power gamer to refer to anyone that does this.
In reality, ZillaPrime gave us some good examples of the worst in each category. It just turns out that it's the same player in his game.
I think if you have a player that goes to such extremes, yes they make the game less fun for everyone else, but it's important to discuss things with them first before booting them to the curb. If they don't fit in with the group, then give them opportunities to change. I'm sure there are other power gamers and munchkins kicked out of other groups to play with them if things don't work out in the end.