> There is a big difference between arguing that radical life extension could have serious social and environmental costs, and arguing that we should execute the elderly.

I agree. Discussing ways to solve those problems would be an aspect of the former, which is completely reasonable. However, at the point where you suggested that society could ban life extension, you started arguing for the latter.

Follow your argument to its logical conclusion. What are you proposing, and what would the effect be? You suggested intentionally withholding a cure for a degenerative disease (namely, aging). How else could that possibly be interpreted?

> Death is not an unmitigated evil, nor is eternal youth an unmitigated good. I don't think that's a radical argument.

It's safe to say that's our fundamental point of disagreement.

Personally, I plan to address that disagreement by continuing to donate to fund the development of effective treatments for aging, as well as the development of longer-term cures for mortality. At the point where those treatments become more widely available, arguments against them will start looking a lot sillier.