That's where you and I fall down and disagree on this issue.
Spraying graffiti on the side of a private building is exactly the same as posting a message on a private social media platform.
If the owner of the building does not like the message sprayed on his private property, he has every right to censor/delete it.
If the owner of the social media platform does not like the message posted on his private platform, he has every right to censor/delete it.
And there are plenty of private building owners who allow graffiti to remain on their private buildings, because they agree with the message being sent, or enjoy the artwork. NYC is a prime example, along with may other large metro cities! But it is THEIR choice to allow it or not, as private owners, and NOT the government's choice.
That's it, that's all there is.
So you think twitter agrees with and likes the messages posted by the Iranian dictator on his private platform? Oh ok. Good to know.