The difference is in the legal definition of protected class. It is illegal to discriminate against someone based on their membership of a protected class -- ethnicity or disability for instance.
Removing an opinion or banning a user based on violation of an agreed upon term of service is not the same thing. Having an opinion does not make you a member of a protected class, and a private corporation is free to allow you or disallow you from use of their services to broadcast that opinion. Newspapers have been doing this since the dawn of print. Google could not, for example, ban someone for being Jewish.
You can argue about whether sexual orientation deserves status as a protected class, but it is disingenuous to claim that the two are the same thing under the law. It is a false equivalency.