Closed platforms have an advantage of being policed by an owner, open platforms can survive only when there’s a governing body and some entity with the function

Closed platforms have an advantage of being policed by an owner, open platforms can survive only when there’s a governing body and some entity with the function of enforcement. People problems are solved with people solutions, not with technical ones. As soon as spammers become liable for every message in the cross-border platform jurisdiction, i.e. the email police can seize their collateral or block their servers by invalidating their certificates, the problem is gone.