To what extent are humans in a technological environment free from natural selection?

Humans in technology environment are not very free from natural selection. According to Charles Darwin, natural selection acts only for the good of each organism, so since our very first human ancestors had no natural defenses, they would die from what is considered today an insignificant disease. It was throughout millions of years, that the human body started to build an immunization to certain diseases and only the stronger humans were the ones to survive and carry on that trait.
Likewise, having no fur on their bodies to survive in the cold weather, they learned how to use other animals’ skins and how to build some weapons, in order to chase wild animals. Nowadays, humans have made incredible discoveries; we have created a wonderful world of technology, which leads us to make some enormous progress in the field of medicine; especially in how to treat diseases which were, at some time, considered incurable. My point is, that since we have made such progress in technology, I am scared that we are keeping too many people alive, including some that might not fit the environment in which they live.
In addition, we are allowing some infertile people to reproduce through in-vitro fertilization, when apparently they were not capable naturally. We are also letting babies survive by saving their lives at their birth even though they might not be perfectly healthy or other traits which could bedetrimental for the human species. But through science and the new technology, we have let these babies live and we have given them the opportunity to grow up and reproduce, transmitting their traits to other generations.

Due to these facts, it is very probable that we are acting against natural selection in human beings, ever since humans became people who think and care for one another and we have made it immoral to kill another individual or to let him die. However, we could think about another definition of natural selection, such as a life on Earth dies if it is not adapted to its environment and it lives if it has a niche and can reproduce in its surroundings, which is also called survival of the fittest.
If we take the example of a fetus in his mother’s womb, the body of the mother can detect some errors coming from the fetus, and it would eliminate the fetus through a miscarriage. So, in this case, natural selection does still act upon human; acting within the womb of a woman, and therefore, not let a human being, which would not fit its environment, survive. For instance, we have not seen any people carrying the traits of Down’s syndrome on the chromosome 14.
It is likely that this defect happened before but only inside a woman’s body which eliminated the mistake through a miscarriage, not letting the future human sees the light. So, in this case, the fact that humans are living longer, letting them reproduce thanks to many discoveries such as in vitro fertilization, surgeries, transplants, medication, etc. , is because we are taking into consideration that the technology is part of our environment.