The insane part is that you think working that late is okay. I'd say you need a union to better negotiate your time, but you're probably a libertarian anti-union nutjob who will simultaneously defend your free-market right to work as damn much as you please while bemoaning the people who say "enough is enough, work-life balance matters more to me than finishing this tonight" and leave at a reasonable time. Hell, if half your company does it, then obviously management is okay with people leaving that early, so you are only staying because you want to and are just trolling for no reason.
(If you start leaving early, and you are called on it, point out the other people that leave early. Just make sure to get it on a recording if they say it's because "they have children" and you'll be set for life if they fire you, since those anti-discrimination laws protect your non-child status as much as it protects their child status.)