back when something awful and metafilter were comparatively big, much of the impetus for the paywalls they put on registrations was to structurally prevent the possibility of this sort of thing. worked fine, although those two communities themselves are pretty moribund.

it would all be solved forever and anon with a paywall. 5 mao men, botheads, shilling, you would raise the cost to them by orders of magnitude (stealing other people's credit card numbers cost real money)