What they want to see, above all else, is someone who can't be easily blackmailed. (Which is one reason why homosexuality was a dealbreaker as late as the 1970s.)
Unfortunately, that's not what I was directly told when I inquired, at least for the jobs here in Aus. Perhaps they were just being conservative about it
(Now, that said, holding a clearance can be a pain for other reasons already detailed in this thread. A lifetime ban on talking about some things can be an annoying cognitive burden to carry, also.)
Of course, if you don't believe in any of the causes you might need a clearance for, it doesn't matter, but don't be too quick to make that assumption either. A lot of stuff gets classified by the government, and not all of it is morally noisome.