I think it's perfectly reasonable to have multiple reasons for doing something. Making money and deterring malicious users are both valid reasons. Some forums have paid fees for the purpose of deterring unwanted users (MetaFilter, Something Awful, Bitcoin Wiki in the past), so it's certainly a strategy with a precedent.
Yes, you can have as many reasons as you want, but the more you list them off to the public, the more time you have to spend defending them individually.. was the point that I was making.
