Ah, that was an assumption made because most folks abstain :)
As you suggested, I'll try again.
If your vote results in more genocide being likely, you have not washed your hands of it.
And that's just talking about a single issue. Like you said, a trump presidency will fuck things up for many more Americans, so if your vote results in that being more likely, that's a choice you made.
What it comes down to is do you care about reducing the harm in the real world, or if you care more about having a clean conscience. Your protest third party vote undoubtedly makes more genocide more likely in the real world, but you get to feel good about not compromising your beliefs, which has its own merit.
If you value a clean conscience over reducing harm in the real world, you do you, I just want to make sure you're aware of the decision you're making.
The person you're arguing with is either wantonly dishonest, insane, or both. They're entirely unreasonable and arguing with them will get you nowhere. On top of that, the audience has moved on. Literally nothing can be gained by continuing the conversation except for frustrating yourself.