Newton and Einstein were absolutely brilliant beyond their time, and would definitely have continued to make great contributions. Overall people have gotten smarter over the generations, but the geniuses of the past would still be geniuses today. In mathematics alone there are dozens of examples of people who were proving things that we still haven't replicated. Just by looking through their notes we have found solutions to problems we hadn't been able to solve yet.

>This is - look, you can't argue that someone has the right to live based on their life achievements. This is like the ultimate perversion of the 'american drem' delusion - just achieve great thing and you can live forever.

I'm very anti-libertarian and totally against the idea that the ends justify the means wrt achievement. However geniuses do exist, and their productivity is very often cut short by death or age. As a race we would have been able to gain immensely if a few hundred people had lived a decade or two longer.