Mining cryptocurrencies is a good way to launder stolen credit cards numbers to cash. It is scalable (unlike most digital goods) and automatable (unlike most physical goods). It being unprofitable will not dissuade anyone from this use case: they are not paying with their own money to start with.

So it is best to forbid it in the TOS and just autokill the miners, rather than wait for the chargebacks. Especially if the compute is being sold at cost, since there is no buffer of profits to balance out the abuse.