I think you did the right thing by staying mostly quiet if you had lost your temper. When you speak, you must say the right thing to be able to convince people. Now you have time (and input from TCS) to prepare a good argument for the future.
Certain people, like pitbull guy, say anything for a response. Like a troll on a message board, the best defense is ignoring him. Nothing you say to him will make a difference. But if it comes up again in conversation, you can use some ideas you prepare to convince some others of the value of cats.
I would aim for a goal of not abusing cats. Who cares if someone likes them or not? As long as they don't bother the cats, right. And the teacher may believe his pets are disposable, but I'll bet someone else at his house disagrees, and that is the person the cat loves!
Don't take it to personally, prepare yourself for the next time this happens. And exhaust your anger with cat loving friends! Good luck, sounds like you are in with an odd bunch!