Being a parasite requires some sort of active harm. Since the cost of obtaining a torrent is essential nil, and the creator doesn't support it anyhow, you're not harming them in the least.
Now, you're also certainly not giving them any benefit, and perhaps you believe that they deserve some benefit, but that still doesn't make you a parasite any more than anybody who just didn't buy a movie.
Put another way: to the creator, the utility of your torrenting a movie is the same as the utility of just not buying the movie. Now, obviously the utility of your paying the creator is higher, but that still doesn't make you a parasite.
You are at worst a symbiont, but there's nothing inherently wrong with that.
Now, there are other arguments for copyright, but your point about being a parasite is just inaccurate.
You're hampering the exclusivity which the creators rely upon to sell their work to distributors, and you're also forcing them to compete against another outlet (bittorrents) using their own work against them. That's pretty harmful.
By your logic, someone could set up a company called PBO which just mirrors HBO's cable feed, and there'd be nothing unethical about it.
Now, you're also certainly not giving them any benefit, and perhaps you believe that they deserve some benefit, but that still doesn't make you a parasite any more than anybody who just didn't buy a movie.
Put another way: to the creator, the utility of your torrenting a movie is the same as the utility of just not buying the movie. Now, obviously the utility of your paying the creator is higher, but that still doesn't make you a parasite.
You are at worst a symbiont, but there's nothing inherently wrong with that.
Now, there are other arguments for copyright, but your point about being a parasite is just inaccurate.