No one says anyone has a right to be listened to. The right to free speech does not guarantee a right to an audience.
The online equivalent of the image I have painted above is, "You go on Twitter and you post something, and nobody is interested and it just gets ignored."
Twitter removing it is the same as someone pulling you off the box and shoving a sock in your mouth.
Until that actual public square exists online, Twitter, while they may have the legal right to silence you, have an ethical responsibility not to - because THEY chose to provide the platform that they knew everyone would use.
If they want ideological filtering they should make it part of the signup requirements.
You are under the misapprehension that Twitter (or Facebook or Google, or any corporation for that matter) has any ethics at all. They exist to make profit. And anything that doesn't align with that is unimportant to them.
I'd also point out that on Twitter or Facebook, you aren't the customer, you're the product. And they keep you in your little section of the feedlot (filter bubble) to keep you pacified and feeling good, as they profit off your PII and eyeballs.