It is difficult to restrain users from posting too often when creating new accounts are free: how do you compete with free? You can't make it worse than creat

It is difficult to restrain users from posting too often when creating new accounts are free: how do you compete with free? You can't make it worse than creating a new account because then the users will just create a tons of new accounts. So somehow you need to make account creation "more expensive" to be able to have a working cost/rate-limiting on posting.