Why are politicians such science ignoramuses?

Listening to the U.S. Congress's leading Republican on ABC's This Week today, I was both amused and annoyed. But mostly annoyed.
There was John Boehner dismissing the very idea of anthropogenic climate change: "The idea that carbon dioxide is a carcinogen that is harmful to our environment is almost comical. Every time we exhale, we exhale carbon dioxide. Every cow in the world, you know when they do what they do you've got more carbon dioxide."
*sigh*
Another blogger explained what's wrong with that statement very succinctly, so I'll just quote him: "(1) No one has ever claimed that carbon dioxide is a carcinogen (2) there are thousands of substances that are perfectly safe at one level of exposure and dangerous at another (say, water), and (3) cow flatulence consists of methane (CH4), not carbon dioxide (CO2)."
What bothers me most about Boehner's idiotic statement is that, among politicians, he has plenty of company in his smug ignorance. It's all too common to hear and read politicians' incredibly stupid denials of human-made global warming. Canada's current PM seems only a fairly recent "convert" to the scientific consensus on the topic.
Then there are those in government caucus in Ottawa who think evolution is "just a theory."
Canada's science minister, Gary Goodyear, tried last month to dodge a question about whether he believed in evolution by saying it's wrong to ask him about his religious beliefs. Then, just to show how much he knows about science (not much), he told an interviewer he believes we're evolving every year.
As Goodyear's foolishness faded from people's memories, a government backbencher made a statement in the House of Commons to remind people of the stupid that infects Team Harper.
James Lunney rose before question period to denounce "an attempt to ridicule the presumed beliefs of a member of this House."
Fair enough so far, I guess. We wouldn't want to hurt Goodyear's feelings, would we? Never mind that the issue was not his religious creed but rather his grasp of science and reality.
But then things got really weird. Lunney went on to dismiss evolution: "Any scientist who declares that the theory of evolution is a fact has already abandoned the foundations of science. For science establishes fact through the study of things observable and reproducible. Since origins can neither be reproduced nor observed, they remain the realm of hypothesis."
Here Lunney's breathtaking ignorance was in full bloom. He clearly doesn't understand evolution as both a fact and a theory. That is to say, scientists have observed an overwhelming volume of evidence to accept evolution as a fact, and they have developed a theory to explain it.
See how that works, Jimmy? No?
Well, maybe this analogy will help you along. Instead of evolution, think about gravity. We all acknowledge gravity exists, right? It's what keeps our feet on the ground and allows us to pee into urinals instead of up into the air.
So gravity is a fact. It's an observable fact that can be demonstrated in reproducible experiments.
But there's also a scientific theory to explain it. See? It's an acknowledged fact, with a theory to explain it.
Same with evolution. Scientists have observed so much evidence of evolution that they accept it as fact. And there's a theory to explain it.
Some have countered that Darwin's theory of evolution by natural selection is on shaky ground since scientists have, over the years, found flaws and modified it.
Well, the same can be said of Newton's theory explaining gravity. That's how science works. Theories are challenged and, if found wanting, either replaced or modified. Our knowledge of the natural world grows that way.
All of the above is mostly me blowing off steam. But I'm still feeling annoyed and frustrated, because I'm not any closer to understanding why so many (mostly conservative) politicians are so woefully ignorant about science.