No, we are not weakening our race by helping sick kids so they can reproduce new specimens of humans when they get adult.
The fact we are so many humans are an evidence of our species succes.
..and in a way failure by the nature, since we are too many and no longer have any natural enemies (except cancer and such things).
Look at rats, they become fertile and will breed before you can tell if they have passed on any bad genes to coming generations, and must rats counts as a succesful specie.
We should be glad that rats dont have the technology of medicine.
EXPERIENCE BY AGING
Experience is an important thing when it comes to scientific and technological breakthroughs that are beneficial for mankind, and if we didn´t had medicine and technology, then great brains like Stephen Hawkings or John Nash maybe not would had survived long enough to think out those great things they did.
And the longer time you spend on this planet the more important things you will learn that you can teach your children, so they can pass on this info to their kids and so on
All aging is beneficial for our specie.
ANOTHER THING
I have worked with physically challenged people all my life, but I was forced back to school now since there are no jobs anymore, there are not born enough kids with handicaps here where i live. Thanks to science.