More importantly the walled gardens can also use those barriers to keep people out. I have been put in Twitter jail three times for POSSEing tweets.
The first time I @ mentioned baseball players when live tweeting the all-starr game. I was flagged for harassment. They never unlocked my app. I had to stop syndicating from WordPress. That is how you treat fans.
The second time I was inviting bloggers of color and developers who identify as female to the #IndieWeb summit.
The third time (currently) I @ mentioned other educators in discussion of owning your own domain and how best to engage with twitter threads. Who knows how long they will lock me out.
The content of my tweets can not be suspect. I literally "copy and pasted" all my offending tweets natively and not one was flagged for "harassment."
Good to know that if you push for better diversity online Twitter's harassment filters will mark your tweets as dangerous.