Neither party is going to let a third party in.
I feel like this is the exact proto-fascist thought virus that makes Americans American. Political parties are not supposed to permit other political parties to hold power,, even if that's not how you intended to communicate the inability of a third parties to win,, it's still a Freudian slip.
If not voting for one political party is an implicit vote for the "opposite" party then there is no party, there is no choice. It's like making the choice to eat or not, there's no choice if you don't eat you die. If you don't vote Democrat you vote Republican, therefore there is no choice (Unless you think it's possible to choose death which I don't think is possible if I want to be consistent with my values).
Even though we know that democracy is not mathematically possible we do know that certain democracies are more democratic than other democracies.
We need preferential voting if we want to improve the situation but if our goal is to go maximum anarco-democracy then just look to that one episode of the Orville where they encountered a people practicing absolute democracy, good show and poignant episode, BAD OUTCOME.
Imo someone needs to be in charge and that someone has to be more responsible than me and not me, and if that's how I lay out my preferences on my ballot then I will have a better government.