Incorrect when accounts are free. Usenet providers are forced to police users changing their email addresses or signing up multiple times, or else they get de-peered. IRC networks do IP address bans.
For at least the past 20 years, Usenet has been so full of spam that it’s been made virtually unusable. If de-peering is an option, then why haven’t the providers that allow spammers to operate gotten de-peered?