We absolutely are not headed towards extinction as a species. We are like cockroaches and the human species will survive. Using "oh no, the human race is dying out altogether and we must preserve it all costs" is a ridiculous argument.

> [..] it makes sense to cause local ecosystem damage in the form of flooding.

It isn't just the (risk of) flooding. It's hubris to believe we can actually foresee all the second-order ramifications from such large-scale terraforming projects. (Hydroelectric) dams have devastated the local wildlife, transformed the surrounding permaculture for the worse, and set off horrible chain reactions with devastating consequences for the local flora and fauna which have global ramifications down the line, as we are discovering today. Nothing happens in a bubble.

This same argument was once made of fossil fuel emissions (when we thought that smog in the biggest industrial cities was our biggest problem and outsourcing them to developing nations was a great win-win /s). That obviously wasn't true. Why would you wish to repeat the same mistake?

I recommend reading actual IPCC projections and analysis rather than whatever media hype you've been fed.