“No matter how much I hate the idea of a president Mitt Romney, I will vote for him in the general election for that reason alone.”
Now we get to the nut of the underlying philosophical difference here. You’ll continue to vote for whatever “republican” the gop nominates on the off chance that their USSC appointments will matter worth a tinkers cuss. If USSC appointments actually mattered, then why oh why is Roe v Wade still the law of the land? Over 35 years later!
The gop is offering conservatives a suckers game. It’s three-card monte for conservatives, and I’m done playing it. I’m picking the most conservative person on the ballot. If that candidate happens to be a libertarian, then so be it. If that happens to be a third party candidate, then that’s just fine and dandy with me.
If the gop won’t nominate conservatives, then what good is it?
Your confusion is based on the idea that libertarians CAN be conservative. They can not. Libertarians are strict constitutionalists. As such they have found a place within the Republican umbrella, as a sort of conscience, but they differ with conservatives on many, many issues.
I am not going get into an issue by issue discussion here, so if you need to know what a conservative then "looks like," pick Ronald Reagan, the benchmark for modern conservativism in this country. The man was not perfect, and he famously (on this website anyway) appealed to libertarian voters in a 1975 interview with Reason Magazine, but as president he consistently chose the conservative pack, as opposed to the libertarian one.
You can be a libertarian republican, or you can be a conservative republican. You can't pick your friend's nose, and you can't be a "libertarian conservative."