That's a stupid and insulting comment. Those "poor, rural whites" (and blacks, hispanics, native Americans, etc., etc.) who serve in combat arms are all volunteers and they are quite proud to be "on point" for their country.
I live in a rural town that claims the most deaths per capita in the Vietnam War. We have a helicopter memorial to them and Veterans Day is the most honored holiday here, with the businesses all closing for the parade, even if it is a weekday.
So this may not be a slur; it may be the truth.