I would like to see an option of giving a warship a raiding liscense (letter of marquis I believe they were called) and letting them go. You would then start getting an income from raiding each turn that they were in another civ's zone of influence, until they were destroyed. You could recall them to your fleet, but you would, of course, loose the income. Each civ that had a raider loose in their territory would loose income equal to what you gained. Destroying a pirate would not be an act of war, but having one of your pirates in another civ's territory would hurt you diplomatic relationship with them.
The Galactic Privateers wonder would make you immune to raiding losses.