Why does Facebook have such radically strict terms of speech to the point where only certain opinions are allowed?

they don't. they simply do not allow people to verbally assail other members. it is a place of Friends, not Enemies.

Maybe you don't fully understand the Community Standards and Terms of Service. Those are the sets of rules that can legally dictate what you can or can't post on Facebook. Free speech isn't permitted there at all because of it. 

All that means any posting that is objectionable in any way can result in a temporary block; persistent violations can result in your account disabled. If you feel they are way too strict to handle, then the best thing you can do is not return to the site.

There is No Freedom of Speech Facebook has Rules that people have to Follow If people choose not to Follow it thats when there Posts get Deleted