Don't know if this chimes with you, falcon5, or with placemat's brother, but in the 2016 US election, a lot of effort was put into voter suppression.
"Don't vote for the result you actually prefer, because X" was a common technique.
Eg, "The best way you show your disdain for racism is not voting at all,"
or "You might desperately not want Trump, but of course you can't vote for Hillary because ."
We know about the Russian and Trump-campaign efforts to suppress the vote, because of what's come out about the Russian troll factory and about Cambridge Analytica. But we should assume it will be a major technique on social media in all future elections and across most parties.
falcon, you blame yourself for what you describe as your "overthinking". But maybe you're a bit less culpable than you believe? I wonder where the idea came from? And whether both you and placemat's brother came up with the same convoluted, counter-intuitive idea completely independently, or whether it was suggested to you at some point?
Whether or not it's relevant in this case, it's a thing for all of us to be aware of in the future.