Obviously this is a bad argument but it's also bad science.
Medicine didn't stop or break natural selection. Nothing stops natural selection.
Our homeboy doesn't point at a beaver dam and fall to their knees, crying out in anguish over how beavers have wrecked natural selection so what's the big deal when we also create things that improve our chances of survival?
People still have car crashes and natural disasters still happen. People die from asthma in the developed world all the time. People that have a disposition towards being too reckless or too aggressive are going to be statistically more likely to die by misadventure. People who are "insufficiently" social are much less likely to procreate.
Natural selection doesn't give a fuck about medicine and medicine doesn't remove selective pressure.
If they want to live in a world without humans changing the landscape that selective pressure exists within then they're welcome to strip naked, walk into their nearest wilderness and subsist by foraging for food without making any shelter or tools. In fact, I'd encourage them to do exactly that because the world would be a better place if the people who invoke natural selection in the place of an argument showed their commitment to natural selection.
