In principal I agree with you. But consider the case of Gmail. You have to communicate with a lot of people that use Gmail, and Google can block that because

In principal I agree with you. But consider the case of Gmail. You have to communicate with a lot of people that use Gmail, and Google can block that because one of their robots decides it doesn't like your host/server/domain/IP/face. You have little recourse to resolve this, probably even less so if you don't have a Google account.