Scenario One: I, a real, active user that discusses a variety of topics, says something someone doesn't like and twitter decides to ban/shadow ban me.*
Scenario Two: I set up a network of fake accounts to automatically tweet, dm or @mention people pushing the same thing over and over to thousands of users.
Twitter has a block/ignore function. That is all that is needed to deal with scenario one in the vast majority of cases. When companies start introducing their politics and speech preferences into a global communications platform in the form of censorship and banning, the utility of that platform drops immediately. Consider if anyone ever said something in an email or sms that someone else disagreed with, we took away their ability to use email or sms. I know it's not apples to apples since those are primarily one-to-one platforms but you can see what I mean.
Meanwhile, combating scenario two almost always has a positive effect, but apparently is too hard of a problem for Twitter and its $2b/year budget to tackle as evidenced by the complete and utter lack of progress on that front since, from what I can tell, the platforms humble beginning in 2006.
*Note this is a hypothetical, my account is and has been in good standing since I signed up but I've seen many accounts go away or be silenced in this fashion.
Edit: Had wrong date for twitters inception. Fixed.