The good news is you don't have to. You're not, afaik, liable for buying an MP3 from Amazon which later turns out to be unauthorized.
The closest I believe anyone has ever come is when an unauthorized copy of 1984 showed up, Amazon zapped it from people's Kindles (and gave refunds, and promised to not do that again). None of those people were in any danger of being sued.
But, how is an average person supposed to tell the difference between iTunes, Amazon, and a "download this song for free" site they found on Google, that just so happens to use BitTorrent for distributing those files?
BitTorrent links don't work without installing a BitTorrent client?
I'm not entirely unsympathetic, but ignorance of the law has never been an effective defense (for any law), and neither has the "but I was tricked" defense. This is not peculiar to copyright law or computer law. There have been some cases where people did succeed with "I had so much malware, I didn't know what my computer was doing", but that's something you'll have to argue in court.
But why should consumers presume that installing a BitTorrent client means that the download is illegal? It's an unjust expectation on the part of the copyright holders. Note that I'm not necessarily arguing with you specifically, but with the idea that it's obvious that some downloads are legal and others are not, as well as the idea that "BitTorrent" automatically means illegal.
When you install BItTorrent, you become a distributor. You better make sure that you have distribution rights for any IP that you are distributing, or you are violating copyright law. That part is straight forward, and has been pretty much settled in the last decade.
That doesn't mean the settled law is right. How is the average person supposed to know that their torrent client is "seeding"? Ask anybody off the street who the distributor is in that kind of system and they'll say it's the one who uploaded the .torrent, just like the distributor is Adobe or Blizzard or the BBC when they use P2P to distribute stuff.
