Did we essentially stop evolutionary progress by using modern medicine?

If it weren't for antibiotics, surgical advances and life supporting devices, most of the crippled, deformed and retarded/crazy people would not be able to reproduce like they do now. Are we ruining it for future generations by perpetuating "weaklings". (Not trying to be offensive here, but can't think of another way of phrasing this question) Is "Survival of the Fittest" doomed?