The party that stands purely on principle will have no power! I don't like it, but conservatives have to play politics, too. That means they might have to compromise on some issues in order to achieve other, bigger goals.
Realistically, there aren't enough conservative votes in the US to win all of the battles.
I think that you have bought into the liberal/RINO lie that we must compromise principle to get elected. There are prominent examples to the contrary. Reagan. Toomey. Ron Paul. Rick Santorum. Daryl Metcalfe. (Who?)
The problem isn't when a pubbie pol stands on principle that his election is jeopardized. It's when he waffles and compromises. When the pubbie acts, campaigns, and votes like a democrat, the voters are turned off and drop out. They don't see a difference in the politicians or that their vote matters in the outcome that they want.
Reagan took the country by storm. Then he really kicked butt in the second race. Bush I won because people were expecting Reagan term III. When Bush I folded, he was abandoned.
Toomey is in a predominately dem district, but he has consistently promoted conservative values and won with respectable margins. Even the dem voters appreciated and supported him because he was consistent and honest. He didn't pander. He didn't promise what he had to intention of doing just to get votes. If Bush and Santorum had the courage of their (stated) beliefs or even just stayed neutral, Toomey would have won the race against Specter.
Ron Paul is the same. He tells his voters (mostly dems), not what they want to hear, but the truth. Do you know that his biggest opposition is from the GOP? They want him replaced because he votes based on the Constitutionality of every issue and not on who proposed it or how popular it is. If we had more men of principle like Ron Paul, we wouldn't have the mess that we have in Congress now.
Locally, a state rep Daryl Metcalfe is the most conservative rep in PA house. He clobbers any dem challenger, but the state GOP constantly tries to find someone to challenge him because he holds true to the Consitution and doesn't waver.
Now I know that in some areas of the country, these men would have a hard time winning, but that doesn't mean that principle doesn't matter. Above all, people, including dem people, want honestly even if it conflicts with personal political beliefs.
If more Republicans were like these men, they win more often, not less and with bigger margins, not smaller. There are lots of people who would gladly vote again if their vote meant that they'd get a man (or woman) like any of the above.