What do you mean, how do I know? It's basic anthropology and history. A dominance-based hierarchy, which is what patriarchy is, is good for the people who hold the power. It's not good for anyone else - and it's also a brand new concept in human history. Here's an informative story that my friend wrote about that:
https://medium.com/inside-of-elle-beau/yes-our-ancient-ancestors-were-egalitarian-b32df87bed57
A story in New Scientist entitled Why Egalitarian Societies Died Out, has this to say:
“FOR 5000 years, humans have grown accustomed to living in societies dominated by the privileged few. But it wasn’t always this way. For tens of thousands of years, egalitarian hunter-gatherer societies were widespread. And as a large body of anthropological research shows, long before we organized ourselves into hierarchies of wealth, social status and power, these groups rigorously enforced norms that prevented any individual or group from acquiring more status, authority or resources than others.
Decision-making was decentralized and leadership ad hoc; there weren’t any chiefs. There were sporadic hot-blooded fights between individuals, of course, but there was no organized conflict between groups. Nor were there strong notions of private property and therefore any need for territorial defense.”
And then there's this as well:
“In a demographic simulation that Omkar Deshpande, Marcus Feldman and I conducted at Stanford University, California, we found that, rather than imparting advantages to the group, unequal access to resources (patriarchy) is inherently destabilising and greatly raises the chance of group extinction in stable environments. This was true whether we modelled inequality as a multi-tiered class society, or as what economists call a Pareto wealth distribution (see “Inequality: The physics of our finances“) — in which, as with the 1 percent, the rich get the lion’s share.
Counterintuitively, the fact that inequality was so destabilising caused these societies to spread by creating an incentive to migrate in search of further resources. The rules in our simulation did not allow for migration to already-occupied locations, but it was clear that this would have happened in the real world, leading to conquests of the more stable egalitarian societies — exactly what we see as we look back in history."
