TOR itself isn't shady, but it is used by a lot of people wanting to obfuscate various things. I would say that despite its ability to visit .onion website (which are the tip of the iceberg for finding the dark side of the Internet), TOR itself is a positive thing because it allows for that obfuscation.
I think the most important one is for political journalists and domestic violence victims, both of whom may have reason to keep something private. The way TOR functions, sort of reminds me of the early telephone operators.
Anyway, my last interesting bit about why I like TOR is that it is used on the Amnesiac Operating System called Tails which can be installed and ran from just a USB drive, and the drive itself plugged into any regular computer is just seen as a standard USB. Since it's amnesiac, the only data on the computer is in RAM and if you pull the USB out the OS shuts down. It can be set up to store data though, for example files or websites. So between this OS and TOR, one could theoretically avoid tracking software set up on a computer from an abuser.
Also there's just a lot of people that like weird niche things. Over 2 million people in Germany use it and it's got a bit over half a million in the U.S.. I imagine a fair portion of that is people selling darknet services of some variety, but I would be surprised if it was even 50/50