This reasoning is absurd. The structure of the site is designed to allow for thousands of forums on subjects as diverse as home brewing to uh, feminism. Saying that Reddit is sexist because it has a "Men's Right's" forum is like saying the internet is sexist because this guy exists (an argument for another day). The differential Adrian ignores is the money. The chick asked for cash, the dude didn't. Shouldn't anyone raise an eyebrow when a stranger asks them for money? On the internet? Chen completely glosses over this distinction because without the sexism angle his argument falls apart.
I doubt it really has anything to do with "reasoning" or "arguments". Don't we have a term for "journalists" like Chen and his co-panelist Rebecca Watson? Ah, yes, that was it.
But okay, so whining about Reddit is apparently a thing now among certain types of vacuous Internet activists. I'm so hoping we can get another hilariously ineffective progressive boycott out of it somehow. Does Jeebus love me that much?