Installing a random root cert to your trust store is a very dangerous thing to do but you're looking at this from the wrong end. I'm not talking about the dangers of a random user installing a random TLS root cert from me I send them over, what, email? That's just not going to happen. It shouldn't happen.
I'm talking about the ability for human persons to host visitable websites without corporate oversight and control. With HTTP/1.1 I can just host a website from my IP and it's good. Anyone can visit. With HTTP/3 before anyone can visit my website I first have to go ask permission every ~90 days from a third party corporation. And if I piss them off (or people who put pressure on them in certain political regions), say by hosting a pdf copy of a scientific journal article, or a list of local abortion clinics, they can revoke my ability to host a visitable website.
With HTTP/3, as a human person, the cure is worse than the "disease".