Decentralisation is best exemplified by email or http. Yes, they enable all kind of things, including bad ones. They behave like infrastructure, just like roads. I enjoy Mastodon because I can find the instance I like best and still be in touch with people from other instances. My instance blocks other instances that they don't like and publicly explains why. When I won't like it any more, I will take my data and move somewhere else without looks my contacts or anything.
Once Nextcloud will have a decent implementation of Activity Pub, I will start my own instance just for myself and I will only see content that I want to see.