This isn't correct and is a common misconception about evolution. The process which does this is natural selection, and it only occurs through the organism being unable to reproduce as well as an organism with beneficial evolutionary changes.
With humans in the modern world, there is no natural selection because of state benefits that keep people alive and able to reproduce who would usually be unable to do so in a world without safety nets.
So in the modern world, any evolution in humanity - either positive or negative - will perdure. In effect we've ended the traditional form of evolution ages ago when we became civilized.
Also, why do you say 'some'? It would stop all negative mutations, as all people are given the ability to reproduce. Your argument seems to be that people with negative mutations would not be attractive, but often they are attractive to others with negative mutations themselves. Or just people who no longer breed purely based on biological fitness - again because of modern civilization.
There is definitely no contradiction there. Genes will still evolve, but it will no longer be through a process of natural finding the most positive genes. Or I'd guess you could say that we will now evolve towards genes that enable the largest families. And the largest families are predominantly in poor suburbs. The actual environment is artificial though, as those families would not be able to survive on their own without support. Taken to an extreme, it would technically be 'evolution to destruction' by selecting for negative traits that make it impossible to survive outside of the safety net. Luckily we're nowhere near that kind of extreme.
What's "positive"?
> The actual environment is artificial though, as those families would not be able to survive on their own without support.
I apologise to those who are offended by my stereotyping - If anything, I'd expect it's some of these people who are most able to survive on their own in the scenario of nuclear apocalypse and all major cities destroyed.
In such a scenario people like software engineers on HN, may even have lack the traits for survival (inherited or learned) - many of us do not know how to fix our own cars or grow our own crops.
Also, the entire world does not have modern safety nets, not even close.
Anyway, by all means, continue smoking if you think it's going to give you some sort of superpowers or immunity that you can pass on to your progeny. Most likely it'll just give you a disease.