I'm elevating this comment from my interview with Rush's lawyer to "full post" status, since it comes from someone who evidently is close to the band and makes a couple of very good points (emphasis mine):
...I've known the members of Rush for 37 years, and like all human beings, their views on a number of issues have evolved and changed. I always find it puzzling when people take a lyric that was written 25 years ago and say "Ah-HAH, now we know what this band believes about X." [ed. note: Good thing they're not American politicians!] The guys may indeed have believed that 25 years ago, and they may still believe it... but unless people know them personally, it's probably not a good idea to assume their views have remained stagnant, or that their views can be totally discerned from analysis of lyrics.
That said, Rush has the right to decide who may or may not use their music. Rand Paul should not take it personally, since the guys don't let ANY political figures use their songs. (And didn't Mr Paul say that private businesses should have the right to refuse service to anyone they wish? Well, Rush, much as I love them as people, are professional musicians and they are involved in business. It is in fact their right to refuse to let Mr Paul play their songs at political events. Oh and one last point-- mom always taught me not to use other people's stuff without asking. Perhaps he suspected Rush might say no, so he never asked...)