Why modern states are unlikely to revive letters of marque

How would the world change if states issued letters of marque against modern pirates?

It is unlikely to work politically or legally because a state would remain responsible for private warships whose conduct it could not reliably control.

Distance and slower information made privateering easier for older political systems to tolerate. Contemporary governments are unlikely to accept the legal and reputational responsibility for private forces acting beyond direct command. A letter of marque would place the private vessel under the issuing state's flag while giving that state limited practical control over each encounter. Modern media, law, and accountability make misconduct visible quickly, erasing much of the deniability that once made privateering politically useful.