Nowadays a "street corner" is you facebook page or your twitter.

If company grows so big that its use is so common - like a street corner - such platform should be available for all - and all should be accounted for their speech also. Platform is a platform, shouldn't policy people around - that is the job of ... police.

Do you wonder why now we have accounts blocked, but when there were people on the streets attacking policy I haven't heard of any account on facebook/twitter being blocked?

It is because platform wasn't free from politics like it should be, companies have preferences and they will block one political view and allow another - this should not be the case if the use of given platform is monopolistic (or duopolistic: twitter-facebook). If you grow you should give up some of your power, the question is at what scale it should happen.

Facebook and Twitter are commonly used, but they are not the street corner. These things didn't exist when the first amendment was written, but printing presses did. And they specifically did not write in a requirement that printers should print anything and everything. In fact, just 8 years after the first amendment was ratified they passed a federal law banning printing of "false, scandalous or malicious writing". And that was fine, because people could still yell on their street corner or write their own letters, which you will always have the right to do.

The explicit calls to specific acts of extreme violence against specific people would be chargeable as illegal incitement if shouted on a street corner.

Then you've essentially got duct* tape over your mouth while your opponents are handed free megaphones

(*duct/duck - delete as appropriate)

We need to get out of the habit of calling these situations censorship and start calling then what they really are: in kind donations. Providing a communication platform for elected officials has a knowable monetary value. There are already campaign finance laws on the books for this situation.