Everything is. The balance between stay and remain within EU is not especially weighted towards remain in an increasing number of countries. The EU deciding to take any sort of a meaningful stance against free speech or free expression is, IMO, much more likely to push those still in the middle more towards leaving the EU than it is to push them towards remaining.

It's an irrelevant act on its own weight, but there always comes a straw that breaks the camel's back. Now is just such an absurdly horrible time to do something that might agitate.

So, banning twitter will directly lead to other countries leaving the EU because twitter is the only way of free speech that exists?

One can only hope!

They did not ban Telegram, so why should they ban Twitter?

Because Telegram complies with demands from law enforcement, despite what they want you to believe.

"ban" twitter how? go to china and ask to license the great firewall? you could restrict it from operating a EU office or servers, you could restrict it from taking payment in euros, you could even restrict EU domiciled business from paying it but actually "banning" it is a much more authoritarian option.

Why should Twitter pay for infastructure for users that don't generate any revenue? That sounds like bad business.

who says you can't still advertise to them? if twitter goes the "screw the eu" route they don't even have to follow gdpr so that makes for a competitive advantage.