Putting legalities aside, how do you expect someone to acquire accounts in bulk unless they are hacking or automating site registrations en mass (site abuse)?
I think you just answered your own question: we would allow people to sell accounts that were registered through automation. Whether or not we ban that is a completely different debate.
I think you're missing the point. Mass registrations aren't illegal (unless it's brute force, or DDoS), but the sales of those accounts are illegal if it's a service account where the registered user is granted provisional access. Selling such service accounts when the user is not authorized to do so (and holds no right to property) constitutes a breach of ToS and is considered misuse of access (illegal). Any user which gains access to the service account is doing so illegally, which is considered illegal access with theft of service.
It's not like selling your bitcoin wallet which you actually own a right to property and therefore you have the right to sell.
You're trying to rationalize illegal sales and theft of service by only recognizing the highly illegal sales of hacked/compromised credentials while turning a blind eye to illegal sales of access codes (invites) and credentials of service accounts, which will then be used for theft of service.
If we actually start to enforce separate TOS for every product advertised here, we would be better closing off the Marketplace entirely. I'm sure most items/digital accounts/ does not allow resale of their products.