I didn't want to derail my help-with-voting thread with a debate, so I am starting a new one.
I should mention than I am a Decline-To-State voter and usually vote for non-partisans, third parties, or people with track records of crossing the political aisle. I am not a Libertarian (tough I share some of their views).
First off, you don't know with 100% certainty they will lose. But that is not the point. If they make a strong showing (like the Reform party did a while back), they could actually set up a possibility of having viable candidates for the following election (the Reform part did get a high profile governor into office).
Some say the way I vote is "throwing away a vote," but I believe that you should not be gaming the voting system to pick the "lesser of two evils," but have your voice heard (metaphorically) instead.
This year, more than ever, fiscal conservatives with socially liberal views can have their voices heard.
If Republicans lose some elections due to having the fiscal conservative vote split (they're likely going to take back the house anyways) , it will make the election next time really focus on bridging that gap. They may let go of pushing creationism in schools, blocking stem cell research, and other such things.
Most of all, they will think twice before they ever try a bail-out of big banks by tax-payers, and may take steps to prevent such a thing from happening again. That was basically socialism for the rich. If you're a Ron Paul style conservative, that was beyond the pale.
The Green party certainly got the Democrats' attention...and now most left-leaning people take environmental issues quite seriously.
A strong showing this year means a possible stronger showing next election, and so on.