This is something I've talked about with a few friends of mine in biological sciences. So many babies/people are being saved by medicine that it's no longer about the strong surviving but also the weak(and stupid, but that's another discussion).
It's a very touchy subject.
I forget what disease it was, I'm thinking Huntington's but I may be wrong, anyway, apparently, some people that find out that they're carriers, choose not to have kids b/c of the odds of passing it, and how debilitating that disease is/can be. I've probably skewed some of the information here, but I'm sure you anyone here will be able to extrapolate the general point that I'm trying to make.
Like I said before though, it's a very touchy subject, and people will scream 'who are you to decide who lives and dies?' or 'why don't you do the world a favour and off yourself' or something along those lines. And while I understand where they're coming from, afaik, I'm not a carrier for any severe disease that ruins people's lives, and also, puts a strain on the rest of society.
Again, I'm going to stress that it's a touchy subject, and I'm not trying to open a can of worms, but it may have to addressed in the future, if conditions in the world change, and we're not able to live with such abundance so as to be able to support the less-than-ables(is that politically correct enough?).