"Maybe."

absolutely.

3rd party voters don't consider....

neither do primary color voters.

3rd party voters are ignoring...

so are primary color voters.

"with the system in place a vote for a third-party candidate is effectively an abstention."

no.

they are probably not going to win an election, but actively voting is the opposite of abstaining.

"It's the desire to make a difference and effectively abstaining that seems incongruous."

they are making a difference by voting for what they believe in, for the policies they consider most impactful on their lives(aka "voting" in most countries).

you see voting as an abstention even though it's definitively the opposite of an abstention, implicitly based on consideration and values.

they probably see voting differently, maybe as an extension of their political will, or a form of activism, or a civic duty to be performed honestly.

I know I do.