Assuming that Desrtopa isn't weird (or WEIRD), it would help if we knew the critical causes of humans' caring about alien values. For example, suppose social animals, upon achieving intelligence and language, come to care about the values of anyone they can hold an intelligent conversation with. (Not that we know this now - but perhaps we could, later, if true.) In that case, we may be safe as long as intelligent aliens are likely to be social animals. (ETA: provided, duh, that they don't construct uFAI and destroy themselves, then us.)