“First, supporters of the Libertarian Party are just as likely to otherwise vote for Democrats (based on social issues) as Republicans (based on fiscal issues).”
Problem right there.
The cost of democrat social issues eventually bankrupts the national treasury, without exception. This is why the phrase “I am socially liberal, but fiscally conservative.” is as philosophically disingenuous as it is intellectually moronic.
What you’re saying is partly true (though if there’s no state-run social safety net of any kind, as Libertarians propose, it’s hard to see why those diseased people would bankrupt anything but themselves and their families), but it’s peripheral to the point I was making contra the notion that they’re “spoilers” who invariably help the Democrats. The Libertarian Party probably attracts as many (if not more) people who would otherwise vote for Democrats as people who would otherwise vote for Republicans. I’d also bet that most of their voters are people who otherwise wouldn’t vote at all.