You'd think that, but with all these Freedoms and Rights we've almost eliminated the ability, nay the NEED to be darwinised.
Those people have the "right" to breed and produce more crackwhores and drug dealers and undermine the economy and corrupt others to do the same, which makes it spread, and the process repeats, because they've got rights to live and have and raise children and ruin their lives (both theirs and the childrens'). They get access to medical care and help by "goodhearted citizens" so they can continue living the way they do.
Darwinism would have eliminated them early on, but since they're allowed to do what they do with little consequence, they just keep spreading like a disease. We have no predators to kill them anymore, we don't smack them down like the flies they are, they stay and continue and create more problems.
Back in the days where we were less civilized, those with diseases and the like were ousted from the group and died quickly from lack of pack safety. The strong and innovative continued, then deemed it wasn't right to be so inhumane and allowed the diseased, disordered, poorly habited to live amongst them and even breed and spread their issues into the gene pool to a level in which there is hardly a child born without some problem.
You may not like to hear it, but that's how it goes. Because we say EVERYONE has the right to live and do as they will, we rather destroy the natural occurances. We save people from their heart attacks caused by overeating, we eliminate the cancer that came to the lungs of the smoker, we illegalize suicide and assisted suicide, even. By emphasizing their right to live, we eliminate their need (or right) to die.