This is an continuation of my last post, specifically a comment from @rufus@discuss.tchncs.de:
It will never get recommended. It’s bad for the network and bad for your privacy.
Excluding that doing so is bad for the network, why it is “private” using VPN but not Tor, inferring from common consensus. The main point in the blog post is a protocol level problem:
apparently in some cases uTorrent, BitSpirit, and libTorrent simply write your IP address directly into the information they send to the tracker and/or to other peers
Tor and VPN are both transports what wrap other traffic within. If that statement is true, no transport can save the information leaking nature of the BT protocol itself.
Tor routes through relays, which could be run by digital rights holders or government entities. Presumably they could trace with some effort. VPN is an encrypted connection to some trusted party who is accepting your money. Some VPN providers have policies about keeping no logs of your network traffic. Presumably the VPN provider needs good lawyers to know they can safely discard and ignore all the copyright notices. If the VPN provider did keep logs, and if they were legally compromised in some way, the VPN would no longer be protective.
The relays don’t have access to the content, it’s encrypted. But the exit-nodes can see what you’re transmitting. They just don’t know who you are because they got your data forwarded by the relays.