[Xcelerate]

I think you're missing his point. The ability to rationalize is what allows people to do bad things. Do you think someone who wants to steal something is going to say "Yeah, this is bad, but I'm going to do it anyway"? Not very often. It's probably more like: "I've had really bad luck in my life lately; I need this to help my family/etc...; One item won't make a difference to the shopkeeper".

So, no, he's not automatically dismissing any counterargument. He's saying that the ability to rationalize anything is a strong reason for immoral behavior.

[S4M]

For me he automatically dismissed the argument of the student giving his reasons to download (he wouldn't buy the music anyway, and the disc production are exploiting the artists).

If I killed somebody and tried to rationalize it (he would have died at some point anyway, maybe he was a bad person, etc.), you could retort that no matter what, I killed someone and it's just bad because you are causing lots of harm (the victim, his family and friends, etc.), but you couldn't tell someone who downloaded illegally some music that it's just a bad thing to do.

That's why I agree with the GP that his mention of the rationalization process is here to automatically dismiss counter argument. It is an interesting point, and I am sure people used this process to have a clear conscience having done really bad things, but it is not by itself a counter-argument to illegal download, or anything else.