Why yes, I am a nihilist. I'm a nihilistic hedonist who chooses to value all types of human happiness the most. It's utilitarian at its core, but I also don't believe in certainty about anything. We can only pick the best option from the limited information we have, and I believe the best option is that which allows people to live the fullest lives. This involves making our short time on this earth as full as possible.

I don't think the person is making a moral error in the decision to vote 3rd party, but in refusing to accept the likely reality. It might not even be a moral error that leads to their stubbornness. They may have been taught something that prevents them from changing their mind.

I don't say "it doesn't matter" because I wish to blame them. I have no faith in those value judgements holding much power. I'm saying that on a mechanical level, the outcome of this vote will be one option or another. We can believe whatever we want about the world, but the world will simply do what it does. It has no reason to conform to our understanding of it.

Not adjusting our thinking to fit reality will keep us from making the best choices. I want progress, not the belief that I'm making progress. The desire only points to results.