So, when you get a stranger being chased by a group of attackers, you can just allow them into your colony, and if you don't like their stats, you can just leave them there and the attackers will take them as a prisoner and leave. So, that means there is literally no reason to decline the stranger, as you can actively check their stats and then make your decision.
Two ways I can see that would fix this exploit would be:
1. On the screen that says the stranger wants to join, it could show the stranger's skills and health statistics.
2. Only two raiders could take the stranger off as a prisoner, while the rest attack the colony.
Tynan has mentioned fixing the taking a prisoner cheese where you can sacrifice a pawn to end the raid. Whether it's implemented in A14 or not we shall see.
Also I've had this tactic backfire on me where I didn't like the pawn, so left him there to be captured but the raiders landed a killing blow then proceeded to raid my base.
There could be a long lasting -10 mood drop for having a colonist kidnapped.
I don't consider this an exploit. It is my colony after all. And the pawn has to survive the onslaught. Very early in the game thugs start coming with triple rocket launchers and they just kill the poor guy or girl. So, again, not an exploit.