I have used Youtube in the past for seeing how to install gun accessories, put guns together, how to fix malfunctions, etc. Watching those videos has made me a more knowledgeable, and hence more responsible gun owner. This is an especially large blow for people who are part of niche communities, like reloading ammo for 100+ year old rifles. A lot of historical content will be lost.
The new youtube rules will also get rid of entertainment channels like Hickock45 and Demolition Ranch (the proceeds of which help subsidize the creator's other channel, Vet Ranch)
I'm also pretty disappointed in Reddit. They made a new admin account yesterday to anonymously post the new rules. I believe this is the first time that's been done for an announcement, usually they're posted by a CEO or a specific individual. /r/gundeals was a fantastic community and I don't know if anything comparable exists elsewhere online. There were lots of links posted by regular users, but when dealers posted themselves they really made an effort to engage with buyers. Crappy vendors/products were usually called out in the comments. Other than optics, I can't imagine why reddit would ban strictly law-abiding communities while allowing illegal and toxic ones to flourish.