There's an argument for it to become a right if the social network intentionally tries to displace other channels of communication and forbids interoperability.
Actually I wonder if that would not fall under Article 27 of UN's Universal declaration of Human Rights:
"Everyone has the right freely to participate in the cultural life of the community, to enjoy the arts and to share in scientific advancement and its benefits."
The human right to basic fairness and reason is generic and applies to everything.
There is nothing magical about social media web services that means it's ok to abuse and discriminate there vs anywhere else.
It also doesn't require a "human right" to say "hey this sucks". That is a valid thing to observe and discuss regardless if the complainer has any special legal rights being violated.