Enforce what?

Why should the ability to impersonate a persons voice suddenly become a crime in itself?

Should we arrest Jim Carrey?

Isn't it when the thing was used to do something else illegal when enforcement is required?

Sure but they can make extra penalties for using these in illegal acts. For example robbing someone, and robbing someone while using a gun get different sentences.

It's already illegal to defraud someone into sending you money.