We have been grappling with these ethical issues since the mid-nineteenth century and the beginning of the Eugenics movement. You have obviously done some deep thinking yourself, and perhaps it is time for you to engage with some texts in history and ethics in order to see how to take the questions further. I suggest Diane Paul's "Controlling Human Heredity" and "The Politics of Heredity" (both cheap paperback books) and an essay by Erik Parens "The Goodness of Fragility" widely reprinted in bioethics texts (there are many other bioethics resources, such as bioethics.net and http://bioethics.georgetown.edu/publications/scopenotes/
Read another response by Miriam Solomon
Is there any validity in the following argument? By medical science we keep people with severe chronical diseases alive and these people are free to reproduce. Already there has been an increase in people with chronical diseases, maybe because of our progression in medical science. So, in the future, it is possibly that we will all struggle with many chronical diseases, unless we accelerate in stem-cell research or genetic manipultaion. With this I see only two opportunities: either deny the chronically diseased to reproduce (Which I think is quite unethical) or "play God" and rid our selves with these plagues with either genetic manipulation or stem-cell research (which is also unethical, for some). But not matter what ethical principles one leans on, these two options are the only sensible ones, of course to the exception of not doing anything (which is also unethical). So we have here, three unethical options, depending on one´s ethical affiliation: 1. Everyone will be chronically diseased. 2. Chronically diseased will be refused to reproduce, and 3. We excel in stem-cell research and genetic manipulation. If you ask me, I would say that everyone would agree that being in a state where everyone is diseased is the least ethical one, we should intervene if we can. The second most unethical option is refusing people to reproduce, as this is a fundamental aspect of human life, without it it could cause mass depression. The third option, although for some is unethical, is the least, because the stem cells that are extracted can not feel pain, and it does not hinder anyone in fulfilling a good life, it only makes some people angry.