threatening to let conservatives further mangle the country when you have a progressive alternative is selfish and incredibly narrow-minded.
And how exactly is not voting doing that when...
the democrats are already winning the votes of young and decided voters
Either the Democrats are comfortably winning (in which case we can vote with our conscience), or they're not (in which case vocal opposition to genocide might encourage them to change policies to garner our vote).
The alternative is that nothing will get them to change policies because they're not interested in our vote. In which case the whole "turn up and the Democrats will move left" theory is nonsense.