> If I were in that scenario, I would behave as you suggest I ought to
Ah, but you don't know if you're in that scenario or not, until other people actually go and vote.
Now, you empirically expect them to do so... but if your response to them doing what they do (i.e. go and vote) is to not vote, and you consider that a rational choice, then why shouldn't others also follow it? And if your ability to make that rational choice is enabled by those others not making a rational choice, I feel like there's still an ethical conflict here, even if you're purely reactive (i.e. is it ethical to rationally "cash in" on irrational, self-harmful choices of others?).
I do know that I'm not in that scenario, in the same sense as I know most things, like that next time I flip a coin it won't land on edge.
> if ... you consider that a rational choice, then why shouldn't others also follow it?
But this doesn't affect my reasoning, because whether or not I consider it rational, or whether or not I do it, does not affect whether or not they do it[1]. Along the same lines, I see no problem "cashing in" on other's irrational choices in general, provided that I am not causing or contributing to them making those choices.
[1] It may affect their behavior in future elections however. It is because of effects along these lines that I ultimately think I should vote.
Ah, but you don't know if you're in that scenario or not, until other people actually go and vote.
Now, you empirically expect them to do so... but if your response to them doing what they do (i.e. go and vote) is to not vote, and you consider that a rational choice, then why shouldn't others also follow it? And if your ability to make that rational choice is enabled by those others not making a rational choice, I feel like there's still an ethical conflict here, even if you're purely reactive (i.e. is it ethical to rationally "cash in" on irrational, self-harmful choices of others?).