That's a toxic way of thinking. No party is entitled to your vote, and not voting for one is certainly not an endorsement of another.
While this is true, very often that is the impact of a third party vote in a federal election. See the election of one George W. Bush and the impact of Mr. Nader.
Unfortunately that is how it works. A vote for the green party is simply a vote not cast for D and favors R; and a vote for a libertarian is a vote not for R, so it benefits D.
A solution is Ranked Choice Voting where you can say, "Green, and if they don't win, D (or whatever)."
Fwiw, I vote my conscience, not to win. Not the best for my political positions maybe, but I hope to send a signal to others that maybe something other than R/D is one day possible. But, yeah, RCV would help with that conundrum.
Toxic?
Trump recently posted a diatribe about ranked choice voting in Alaska (calling it "disastrous, and very fraudulent").
Do you know why the modern GOP hates ranked choice voting? Because they rely upon getting clown votes wasted on the Tulsi Gabbard, Jill Stein's and Kanye West's of the world as a way to get elected. They just need to entice just enough fool-vote drawers, knowing the cult will not sway an iota.
Maybe if the US had a sane voting system, but they don't. I'm of the opinion that their flawed voting system is a huge factor in why the US government is the way it is.