What's wrong with trying now? (By "now" I mean, "in the next 20 years".) So long as nobody gets killed, if it fails, at least we can say we've tried. Trying now may bring forward the date at which it is actually feasible compared to putting off trying.

Even if people die–and they may–if they make a free and fully informed choice to sign up to something which may risk their lives, and they end up dying as a result – wasn't it their right to take that risk? There are a lot of people out there, who will view being one of the first humans to attempt to live on another planet something worth risking death for.

The problem is that it's a massive waste of resources, in terms of fossil fuels, production capacity, engineering talent, research talent. There are much more pressing and likely to be fruitful avenues of exploration. Launch or build telescopes to explore space, and engineer green energy and carbon capture solutions on Earth.