There are some conservatives who think by actively defeating Republicans at the polls, the GOP would then cave in to all of their demands and promote a more conservative agenda in the next election cycle.
Per last annual Harris Poll on political trends, February 27, 2004
Conservatives 33%
Moderates 40%
Liberals 18%
http://www.harrisinteractive.com/harris_poll/index.asp?PID=444
It's anti-conservative to believe that 33% of the country should be able to rule it as if we were King... even if we DO have the best ideology ;-)