@davidbarlow Many fair points - the mermaid in particular (I admit that I forgot about that part).
It's a bit off topic, but being a prisoner IS being a slave - you lose your freedom and what happens to you is entirely up to the whim of others; looking at the American prison system is proof enough of that - slavery, still exists even today. It's just hiding out in the open. I'll say no more on this part of the subject - just rumenate on what I've said, and if you insist on continuing this aspect of the discussion, please PM me or message me via XBL.
I'm mostly concerned about the fun and balance factors. It may sound like fun, and it is, at least for the captors, but not necessarily for those being captured - for them it's more wasted time and work. Imagine grinding for hours, when you're finally about to grab the chest of legends, but then you get knocked out and taken prisoner. Now, you gotta go through the hassle of being ridiculed and taunted, and attempting to escape. And worse, there would be nothing stopping them from doing it all over again. It's bad enough being welayed if they kill you, sink your ship, and still doggedly pursue you - this new dynamic that you're proposing adds a whole other complicated layer upon that.
Besides, if there was a way to end a fight early, say with a 1-hit KO from behind for example, then what's to stop players from double-teaming you from the front (the distraction) and back (the trap)? Fights will end quickly, but your misery won't. It'll be the DGE all over again, but worse, because you'll be captured instead of simply respawning - at least with the latter you get a reprieve, as well as a chance to immediately fight back and/or save yourr boat from sinking and loot from being stolen.
I can already imagine a prisoner transport - a fully-crewed galleon that specializes in capturing players just because they can. What's to stop them from capturing more than 1 person?
Another way to look at it is from the viewpoint of the captors - aside from the things they already get for offing other players (their loot for example), what would be the point? All you'd be doing is taking a calculated risk in the near future (because you know they'll try and escape) with virtually nothing in it for you. Also, because you'd be stealing player's valued time, they'd be more likely to just up and quit instead - mark my words: if implemented, the number of quitters and players who drop the game entirely will rise dramatically (higher than the tallest of tidal waves).
I'm also against the idea of other pirates having the ability to steal the gold I've already rightfully turned in or earned unless I personally choose to take that risk (e.g., like gambling with a poker hand). With your methodology, that choice wouldn't even be up to me. Again, this opens up a whole new way to troll people, and out of their lifetime earnings no less! What's to stop them from taking the next step, and stealing your dubloons too? No - steal my loot if you want (you can certainly try), but you'll never get my gold.
Bottom line - it breaks the game and would be nowhere near as fun as you think it is...