I myself am not a conservative, but I have run into the same issue you have. To be fair, I have also run into examples of blinkered liberalism as well, but that was only in college (where a professor angrily corrected a student who said "the Greeks excelled at horsemanship" to say "the Greeks excelled at horsepersonship.")
Not to get too technical here, but I think the issue often comes down to argument styles. I have noticed that often conservatives argue in what would be called the "classical" argument strategy. This strategy allows for no compromise and looks to build an impregnable fortress of ideas. The problem here is that this kind of argument cannot allow a single concession for fear of the entire edifice crumbling down. It's akin a little bit to religious fundamentalism and literalism. On the other hand, I myself prefer Rogerian argument: allowing certain concessions to build goodwill with my "opponent" and looking to find common ground.
I don't see that a lot in current conservative political thought. Regrettably, I am also noticing that liberal politicians are abandoning the Rogerian style and drawing their own battle lines.
The "President Obama was not born in the U.S." meme that is, amazingly, still alive is a great example of classical argument theory. You'll notice that NOT ONE of the conservative pundits has backed off from this. There is a certain immunity to facts and reality one must cultivate to hold certain conservative views (and for that matter, liberal views), and this immunity is not seen as insanity or unreasonableness, but as a laudable resistance to the other side. I imagine that if you tried to argue with your relatives about that one issue, even if you had a copy of the certificate in your hand, you would not meet with success. It is more important to some people to hold a certain ideological view DESPITE facts--and this attribute betrays a fragility to those very same "bedrock values" that one purports to support.
In short, a classical arguer cannot give up even a single point, lest it call into question their entire argument. A six-year-old boy cannot allow that his mommy can possibly be wrong in any way, because if she is, then she might not be perfect and therefore will be unworthy of his love. A mature twenty-year-old allows that his mother raised him to the best of her ability, and while she made some mistakes and has some flaws, she is all the more worthy of his love because of her success desipte those flaws.
Anyway, that's my additional rant to your rant.