Violence to Target the Violent

This is a little contraversial and I wasn't completely sure where to put this but Social Issues seems like the right place.

This was originally discussed in my History class relating to Nazi Germany and thoughts amongst Nazi supporters, it drifted into a more Philosopical than historical lesson.

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Imagine an area in a city, and in this area there are only bad people, drug dealers, murderers, rapists and general scum of the earth. In the area there are no good people only those who cause hate and misery.

An idea is thought up, if there are only bad people in this area what would we lose if they all died?
What if a squad of soldiers were sent in to kill all those in the 'area' thus removing that stain of society.

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This question was put towards our class to see how we would react and what our opinions were on this issue (you can see the relation to Nazi Germany in the question).

Thankfully we all said it was an evil act that we had no right to undertake, we replied with what right did we have?, whose moral ground are we working from ?, does violence ever solve violence ? , were we as bad as those we would have murdered with if we had agreed ?

What do you think to the scenario, what are you opinions and thoughts....

I would have thought this would have gained some interest due to its potential to create conflicting view points between moderate and radical members...oh well