This question came after seeing CloudFlare captchas, forums outright banning Tor IPs to protect themselves from malicious traffic, and all manner of hurdles where sites simply don't want Tor traffic.
This gave me a theoretical question - if everyone was using Tor, and sites couldn't distinguish between users based on IP, how would they protect themselves from spam and malicious traffic? Would they simply have to accept that there is nothing they can do?
Or would it be in such an alternative reality world that you need to enter a captcha for every site you visit?
I found some similar questions, such as How to protect against DoS but not harm Tor users and How to best help site operators protect themselves from Tor based abuse?, but I believe that mine is a little different because I'm curious what would be done in a theoretical scenario where everyone uses Tor, so blocking it is not an option.