There was a great Freakonomics podcast[0] where they interviewed a Koch brother. It seems like they truly believe that is what would be best for the country. They are Libertarians and believe in it's tenets to their core.
That's pretty much my take on the Kochs as well. They seem to contribute to things they believe in, which incidentally includes public radio stations and hospitals [0]. You may not like their politics--and many do not--but so far everything I have read or heard about them supports the notion they are sincere in their beliefs.
The problem is not so much the Kochs as the fact that we've permitted a political system to arise in the US that allows a disproportionate amount of wealth to flow to a relatively small number of people and to allow those lucky few an outsized influence on the evolution of said system. Those two things are not unconnected.
[0] http://freakonomics.com/podcast/why-hate-koch-brothers-part-...