Why letters of marque could return only in a severe shipping shortage

Are letters of marque still legal, and would a government issue them?

They may remain theoretically possible, but only a major war and serious shortage of naval forces would make their use plausible.

Letters of marque may still be theoretically legal, but the surrounding laws are complex. Governments historically relied on privateers when they had failed to build enough warships before a conflict. Modern vessels face a higher technical barrier to becoming competent combatants, but commerce raiding does not require defeating front-line warships. Privateers would still carry mixed equipment, weak fire coordination, and limited survivability, which is why states prefer commissioned ships they can control directly.