Once the lead starts flying, you don't want "light" separating you from the hot lead, and the "lethal lite" doesn't break the other guy's heavy so well. In the end, it will get you killed.
People want "light and lethal" because they don't want to deal with heavy air and sea lift required to the get the heavy stuff to where the bad guys are. But heavy lift ultimately wins wars.
How true if your not fighting within your own borders. Since 1945 our beaurocrats and lawyers have been steadily whittling away at our merchant marine until now it is almost non-existent. What would be the lead time to build that back from scratch with a couple of shipyards?