I thought that the Founders' biggest worry about a standing army was that it might interfere in politics. But with a professional army, we haven't had any problem at all, especially seeing how many problems France and Germany had because of it.
Not exactly. They were afraid the government would use a standing army to enforce its will on the people. And it has been used in that way before, just as predicted, though perhaps not as frighteningly as in China. But it's also worth pointing out that a standing police force with paramilitary training fills the role the founders feared of the military.
In other words, if you want to know exactly what the founders feared, look at no-knock and warrantless searches, asset forfeitures, brutality in prisons, etc. Today, we don't even bat an eye when a cop calls non-police "civilians". There was a time when that was seen as a very disturbing trend...
An interesting topic . . .
I've read that one of the major reasons men like Samuel Adams etc. were so opposed to royal troops occupying Boston following the Stamp Act Crisis was that royal troops were given police duties there. Boston had no police force or constabulary of note, so regular lobster-backs were given the duty of enforcing the law. Perhaps they feared that a continental standing army would perform similar duties . . .?