A bad person that many people believe to be the bitcoin creator can probably deceive people and extort money from them, heck people send funds to dummy/scam celebrity accounts to double their bitcoin for them, not to talk of an account or a person they think is Satoshi, you are correct on this that he may extort funds from people.

But what the person cannot do is perform any illicit operation on the bitcoin protocol, even satoshi himself cannot successfully do that because bitcoin is not under his control, any illicit operation will be rejected by miners/nodes, that is why decentralization makes bitcoin very unique and safe.