People that download torrents don't give a fuck about its "authenticity".
Nothing's "free" to the extent that people wouldn't care if it's crap. Actually, there's a nice analogy: that flaming bag of dog doo on your porch was likely free too, but it may cause damage. Is it a non-issue because it's free?
Downloading is asynchronous. It may cost some computer resources, but probably not any which you would not have used anyways.
You're missing the point. It's practically free, certainly much freer than the retail price. And usually finding the illegal version something (that's worth it) is just a matter of time.
People illegally downloading don't care about authenticity because it's practically free and is worth it to them. Obviously if the time it takes to acquire it illegally over legally is more than its worth to the person, he/she wouldn't do it (or shouldn't do it), but for the majority of people it isn't true.