Marginal people are at the greatest risk for violence directly stemming from the factors that pushed them to the margin.  By not allowing a 'place' - however defined and implemented - for marginal activities society, and the state of which it is a reflection - is actively increasing the already higher risks and therefore the actuality of the violence.  To meet this society needs to give more physical protection, lowering the risks, to the marginal while doing what is possible to move the person to greater coherence with society.

That is not going to be possible in every individual case.

So what?  

Murder is murder and to knowingly allow the marginal to face the certain risk of death and do nothing about it when there are known solutions is morally loathsome.  

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre