The point of being an admin is that you can edit and change everything that is posted. If someone does something illegal on your instance, or they’re posting stuff you don’t like (racism, homophobia, etc) you need to be able to fix it.
Admins have always been able to modify posts. See Reddit, forums, etc.
It’s a total pain to have to go into the community, scroll all the way down, and then get an error message when you click the block icon. Or a login screen. It should be possible to block communities from the front page.