Why Have Mercenaries?

Why have Blackwater? Here is an answer that applies to both political parties (and is a major menace to our future as a democracy):

"There's a cynical answer and an honest answer," he said, "and I think they're the same answer." He said that the Pentagon is useless to politicians because it doesn't make campaign "contributions". But when you take a big chunk of that enormous military budget and give it to private companies, you free it up to come back (some portion of it) to politicians every campaign season.