I stick with TV-series, and I've never seen an infected file. If I had been downloading software, sure, I would have been slightly more worried, but even so most sites have comments and ratingsystems. Looking at them probably helps you find out if a torrent is malicious or not.

TL;DR-version: In my experience, with some sense, your risk of running into malware in torrents is slim.

That's because you're knowledgeable enough to not click on the misleading ads yelling "download here". Average users might not be.

Offering a safe easy medium does have an appeal to many users, as shown by the success of Steam.

How would you know if a program you downloaded had been modified to send files from your hard drive to a server? I think it can be easily done without an antivirus noticing.