Anarchism wouldn't' make any difference. The rich and powerful will still have the men with guns.
And the poor, who are by definition more numerous than even the praetorian class, will also have guns. If it comes to a shooting war... well, there's a reason kings don't have a lot of power anymore. 
George Orwell actually wrote a great article on this issue, a couple of years before he wrote 1984.
He agreed with you, and said that the emergence of guns (muskets) shifted the power from the view to the many. From the elite to the people.
However, with the emergence of weapons of mass destruction (the atom bomb had just been invented), he predicted that since the power would shift back from the many to the view. Makes sense, he argued, because it would put the weapons back in the hand of the elite.
And look at what happened.
I haven't got the time to find the article for you right now though, sorry.