There are lots of kinds of trolls, i wont pretend to know them all. They dont all care about price, but most do. Those who dont are just attention whores and go around trying to get a rise out of people. The main kind is the ones who do want to drive price down, and try to make bitcoin old news.
Picture this, guy(pre-troll internet user) sees pretty girl(bitcoin), unfortunetly the guy cant work up the guts to ask her out. When someone else does, and they are in a relationship, guy is jealous and begins calling the young lady abunch of names and lies in an attempt to lessen her attractiveness.
The main attack a troll makes is not ruining reputation, it is silencing discourse by interupting thoughtful discussion.