As a species who depends on this planet for sustenance, we have already surpassed the point at which the planet can sustainably feed every human being that exists. I appreciate a lot of the modern conveniences and advances in medicine, but at the same time I can objectively look at the condition we are in today and realize that if we don't colonize another planet soon, or figure out how to build cities under the ocean, a lot of us will gradually starve to death. It may not get to that point in my lifetime, but we're headed that way.
Because of things like vaccinations and advances in medicine, illnesses that would have killed people, and therefore helped to "cull the flock" a hundred or two hundred years ago, are now either extinct, or no longer a legitimate threat. People are alive today that would have been too mentally or physically weak to survive the rigors of day to day life if they had been around at the time this country (U.S.) was founded, and that was only a few hundred years ago. However, even though that is now the case, the vast majority of people, especially those in the lower income brackets (I live in a low-income area, so I know), have not modified their breeding habits to account for the higher chances of survival of their offspring. People continue to have 3, 4, and 5 children, and they will be praised and told how good it is that they can produce lots of children. In turn, each of those children will go on to have 3, 4 and 5 children, so in 2 generations, what started out as one man and one woman, may turn into 20 or 30.
As things stand now, even though the risk has drastically been reduced, there is still some risk involved in the child bearing process. Women regularly have miscarriages for one reason or another. Some people are just plain sterile and can't have children at all. This, in my opinion, is all part of the process of natural selection, and is a vital part of controlling the population of the human race. If we become capable of producing children at will with no real physical effort or pain on our part, the next thing you know we'll be trying to find a way to systematically execute people based on arbitrary divisions that we create like race, skin color, religious background, political leanings, income level, etc., just so the rest of us can have a bite to eat at the end of the day.
Unless of course the scientists that have figured out how to mass produce babies have also figured out how to colonize Mars, then we're all good, :-)
Sorry, I don't mean to disregard your whole post because I do agree that overpopulation is/will be an issue. However, I feel the solution to such a problem does not lie in avoiding technological advances. If overpopulation becomes critical, it's simply a matter of coming up with restrictions to control population growth, e.g. you're only able to perform this procedure once every x years. That's far easier and dare I say it trivial to solve compared to actually terraforming Mars.