This is not offering your house for it. That would be if google was actually hosting their site on its servers. In this case it's a domain pointing to their content. As a registrar Google is serving the public and I doubt you can deny someone this service in a moral sense. Can a doctor deny to treat them if they end up in his office for serious injuries? What if all registrars deny them, is it morally right to effectively erase them from the internet for simply expressing their thoughts?