From a blog post about moral philosophy:
One of the big shifts was from the medieval system of “mostly super-well-trained professional warriors ie knights matter in projecting military force” to “any warm body with a gun matters”. That gave the common people a new level of power and probably led to democracy and the democratic virtues of equality and freedom.
This sounds untrue to me, but I don't know a lot about history. Modern militaries have professional, full time soldiers and knights were basically reservists weren't they?
Perhaps there's a problem with the term "skilled". Any soldier having to wield a sword, longbow, or lance would have to be not only skilled, but quite strong. Guns do not require strength. There are only going to be so many strong men available in a population, so an army equipped with firearms could be bigger. Someone using a sword would also, like any athlete, be at his peak in his teens and twenties, and his endurance would begin to fall in his 30's. Someone with a firearm could go on longer.