That word, i do not think it means what you think it means.
In this instance, the US right to free speech just means that their free speech will not be abridged/removed/prevented by their government - (First amendment)
Non-governmental organisations are under no obligation to care at all about your right to freedom of speech under the law.
However, in this case, its essentially a business decision, one caused by TDS - since the last people to host them got accused (by TDS) of supporting their white supremacist views - which has now meant that any further registrar won't work with TDS because they don't want all the flack that comes with being branded a white supremacist supporting organisation.
And, since being a white supremacist isn't a supported classification under the discrimination laws, they are fine to do so.