They do come from the lower classes, for a variety of reasons, and they are not always the sharpest tools in the shed.
Not everyone leaves school with a ton of options, opportunities, and good advice. That's the reality for working class people. What the hell's so "progressive" in making derogatory remarks about these people you dismiss as "the lower classes"?
Besides, if the army weren't filled with these "lower class" volunteers, the government would almost certainly have drafted your precious ass by now. You might want to think about that for a while.