"equally unacceptable" is not what "no preference" means. i'm astonished you're trying to argue these are equivalent.
"differently unacceptable" is also a terrible situation though! this is the entire point of my argument. I may find some candidates more bad than others. being forced to vote for less bad is still being disenfranchised to a significant extent.
No, having the opportunity to vote for less bad is being enfranchised. The franchise is an entitlement for to have an option you like provided for you by someone else, not is it an entitlement to have your most preferred option be successful through the filtering that happens in the political process you are entitled to participate in before the stage of a general election ballot is reached.
FPTP is a bad system of aggregating preferences where there are more than two options in principle, and produces bad effects in the filtering (and voting) process because people adjust for the bad way that it aggregates preferences. And there are lots of sensible, obvious, and proven ways to make that better. But none of them guarantee you a situation where you aren't forced either to not vote it to vote for a less-bad alternative (though ranked ballots methods move some of the filtering process into the general election, down-ballot votes are still votes.)
the voting franchise is a fundamental right of citizens in a democracy. the fact that you're referring to it as an entitlement is misinformed, and in fact, quite warped and reveals a deep misunderstanding of our form of government.
the state we find ourselves in this year is abundant evidence of the terrible malfunctioning of the American political process. the system we have in place now struggles to reach even the basic requirements of legitimacy and consent of the governed.
what does popular sovereignty mean anyway if large majorities of the populous are very very very unhappy with their government?
"differently unacceptable" is also a terrible situation though! this is the entire point of my argument. I may find some candidates more bad than others. being forced to vote for less bad is still being disenfranchised to a significant extent.