right but hows that any different from 6am and 6pm. Yet some people say all the time "My flight leaves at 1230 at night"
It's very different - it is an arbitrary rule that decides that 12:00am is midnight rather than noon.
OTOH 6am vs 6pm is systematically evident, though that doesn't stop the occasional tautological "6am in the morning" (eg lyrics of Moonlight Shadow), of which criticism is entire reasonable.