I'd wager that the majority would have issues with shooting a fellow American merely for money.
All they need to do is be persuaded that the people they're shooting are "liberals" and they'll have no problem with it.
These people are heavily indoctrinated with rightwing propaganda, where it's the "good Americans" vs. "Godless commie pinko traitors"... you can read plenty of this type of stuff right here on this board.
They won't have any problem shooting "troublemakers" (anyone who opposes the Dominionist agenda that Blackwater embraces) because they've already been conditioned to believe they are traitors and "not real Americans."

