Accepting unwanted money from someone can have serious consequences in many cases. In some cases it is illegal - for example, accepting certain types of politic

Accepting unwanted money from someone can have serious consequences in many cases. In some cases it is illegal - for example, accepting certain types of political donations. In cases where you've been sent unwanted money your obligation is typically to return it, but that specific type of use-case is often not considered when people design things. If you end up in a situation where anyone can send you money and you can't return it, you're in big trouble because the sender might be causing you to unintentionally get involved in a violation of the law and leave you without any method to undo it.