This response really seems to indicate unfamiliarity with this game franchise and its content. Playing the earlier installments routinely involves greater violence and criminality.
If he's fine with simulated murder, assassination, aggravated assault, carjacking, and (can't remember if it's optional or core) beating up sex workers, it's at least strange for him to stop now and object to killing armed opponents simply because they're agents of the state.
To complain specifically about the opening scene of 5 is nonsensical in context (ie: to anyone who's played these games). That's why it's getting mocked.
You're missing the context of the content of the games. They are famous for greater violence and have been for a couple of decades now.