Actually, Hawk -- that's actually the scenario I was going for. Make trade and piracy a group activity. If there are more pirates than trade ships, the trader is toast. If there are more trade ships than pirates, the pirate would be wise to step aside.
If there are equal parts trader and pirate? It's a fleet battle.
Everyone wins.
EDIT: It'd also call for revision of tactics. Pirates would have to strategize their stop points a bit better so the newly armored and armed trader can't run and gun his way to a safe haven. They will in turn group up, which is not a far cry from current piracy tactics. They generally have it more together than a lot of military players. Traders in turn would do well to group up, and with their newer, better guns and more robust defenses will provide ample support for their escorts and each other.
New tactics will be written, people would be more willing to talk, and more scenarios will turn into the Wild Bunch.
There are enough pirates that adding police/military players to this equation is almost a non-factor.