Here's a big part of it, and it ain't pretty. First, while gender may be "a social construct" it tends to recur in similar patterns across most societies. That

Here's a big part of it, and it ain't pretty. First, while gender may be "a social construct" it tends to recur in similar patterns across most societies. That's not to say that gender roles don't exaggerate the (actually very slight, in biological terms) differences and aren't a source of much injustice. However, there's a recurrent ranking that societies create: high-status men > high-status women > low-status women > low-status men. This is why conversations about gender and "patriarchy" fall flat, it's why feminists and MRAs both have a point, and it's not how things necessarily should be, but it's how things are in at least 90% of the societies that humans create. High-status men have harems of 10+ wives, in pre-monogamous societies, which means that some men will have zero. Since women have a rate-limiting reproductive resource (i.e. a womb) they have a good chance of getting at least some action. Low-status men don't, because they're the lowest of the low. No one likes them. And in a non-monogamous society, they're recognized as an actual danger. Of course, most young men will start out low in status. When's the last time, in popular culture, you saw a teenage male portrayed in a positive light? Most of the world fears and hates (most) teenage males. Eventually, the high-status men recognize the threat. They see men who are sex-starved and poor and deprived of opportunities for improvement, but young and fit while they are fading. So they encourage them to raid other tribes, escalate petty conflicts into moral causes, and even glorify the whole thing because it brings the male population down and makes a pre-monogamous society (which would otherwise be unstable and violent) stable for a while. This pattern is so ingrained in us that we've mythologized it and glorified something that is actually pretty awful. It's also where we get the need to "become a man". Because the gap between high-status (or, at least, realized and mature) men and low-status ones is so severe, we've had to create narratives around it. We've also had to elevate quixotry to a virtue. You see this not just in war but when the stakes are smaller. Take startups. What do we call those (oddly nostalgic, even if things were awful at the time) narratives about low-status men working 90-hour weeks, debugging others' awful written-to-deadline code, as 0.02%-owners of a startup whose benefits would accrue to high-status men (founders and investors)? "War stories." As a species, we've had to create this narrative to explain something that we do to each other for Darwinian, reproductive reasons. It continues even in a mostly monogamous and mostly peaceful society.