In reference to your first question, one is acceptable to almost all of society, the other is abhorred by almost all of society. So you can make your own mind up on that one.
Criminals are not abducted. The societal contract is laid out clearly in law. So after committing a crime one knows one may go to jail/prison as the penalty. They are not robbed of their life as a free person. They chose to do actions that entailed a clear penalty.
The whole point of jail is that it is meant to be good conditions to rehabilitate the prisoners. At one end of the scale you have some European prison systems that do this amazingly well, with very low recidivist offender rates. At the other end of the scale are some third world country prisons where the prisoners are kept in horrendous conditions. These horrendous prisons should not exist. If this is the state of your local prisons then you need to lobby to get it fixed.
You might argue that if we legalise murder as a punitive penalty then they are choosing their path if they commit the crime - and that would be valid if we legalised it. But you argued the point as a corollary to abducting and imprisoning as a crime - so you'll have to change your stance to argue that (which I'm fine with). And even then, it still doesn't make it right.
People get it wrong - all the time, they'll fuck up and kill innocents, or they'll simply murder an innocent and say the victim was doing something they shouldn't have been doing (and dead people don't argue back). And I expect the second example will happen a lot.
This is why we have due process instead. But even due process gets it wrong some of the time. So then once again you're killing innocent people.
There is no them and us - so "they" won't destroy society, we all will if we don't act accordingly. And making prison systems instead of torturing, maiming, or killing people who have wronged someone else is a mainstay of "society".
Consider, if we allow murder to become super easily justifiable by persons committing it, will you be at the top of the food chain? Or will you end up a victim? The numbers don't look good for your average Joe in this situation.
Do you want "The Purge" to be reality?