Not voting for them sends a message, but it’s the wrong message - and that message is that the populace prefers the GOP
Hard disagree on that. That's assuming the intentions of the people. https://en.wikipedia.org/wiki/You_are_either_with_us,_or_against_us
If you're argument is that we need to be doing what's right and pushing for progress, then why is that cast as something ONLY the "blue" can do? I don't know how old you are to see how many times the "blue" has absolutely failed at their job, failed the people, but for no other reason than they're in the right party, they keep getting voted in. But I've seen several "blue" presidents do anywhere from fuckall to the bare minimum in terms of progress/change.
There are other options to vote for that don't just include the GOP as you seem to suggest. The US isn't supposed to be just a 2 party system. It's supposed to be dynamic; these parties are supposed to die off when they no longer represent the people. If you want progress and change, but keep doing the same thing that doesn't seem to be all that progressive.... are you making any progress?