No one is obligated to do anything. The admins run the site and they can moderate how they feel. As a user, I can join their site or another one if I choose to.
My opinion of defederating is that it should only be used as a last resort. Taking a liberal approach to defederation means that a small amount of bad faith actors can completely shut down an instance and make it a pariah on the fediverse.
I agree, it's a useful feature for certain people. I'm just not a big fan of site admins making the decision for you. It should only be used as a last resort IMO or to protect yourself against illegal content, CP for example. Normalizing defederation between instances can be abused by a small amount of bad faith actors. If you as a person don't like a certain culture on an instance or community, just block it yourself.