Because it's logical? Arguing that the constitution can mean whatever you want it to mean renders the constitution meaningless.
Do you honestly think that the "Founding Fathers" were able to account for the issues that would come up 200+ years after they wrote it?
This; that said, that's why there's a provision for amending the Constitution. We don't do it enough, IMO.
Strict constructionists focus too much on a minarchist intent, and that's simply not what the Constitution was designed to do, it's there to espouse broad principles. (And I'm a minarchist saying this.)
