It's this kind of Orwellian rewriting of history. "Misandry" was initially mostly a reaction against feminism, that said "But what about men?!?!? Men have it bad too!!!11".
It's like saying "Women are so revered that they're always portrayed as being right. This isn't patriarchy, it's matriarchy!!111". But then nobody believes them when they complain of being raped or sexually harassed and calls them undependable liars.
Yes sure, that's not what it has to be about, be it tend to be that way. The fact is that people rarely complained about misandry before because well... probably it never really existed or the points were too minuscule to be mentioned.
Well fine, stop virgin-shaming for all I care, but what caused Elliot Rodger to an act of violence isn't likely because he was virgin-shamed.
There are a lot of possible factors, but I would suspect it has more to do with his narcissistic rage, his feeling of entitlement and his chronic envy of others. And the fact that he was a part of a hateful culture that promoted violence against women and the society in general that do not share their views.
It's somewhat relevant, because we're essentially talking about the why of virgin-shaming. If a man gets shamed for being a virgin, then why?
Typically, getting laid is an endgoal for men. That is the "prize". This will eventually mean objectification and de-humanization of women.
If sex was about say, love, then why would Elliot Rodger kill them for being unable to attain his "prize"? So even if he were affected by virgin-shaming, the entire culture of male virgin-shaming that is misogynistic in nature is what drove him to violence.
What if virgin-shaming was misandric? Well then we would dehumanize men, and maybe say that men should only be used as a tool to give pleasure to women or give them money or something. But this would be less likely to end up being violent.
So the fact is that women rarely "use" men in that way, as a tool in the same way that men do. This is why misandry occurs less often, because it seems as if men's hatred and women's hatred show up in completely different ways. "Misandry" exist in women very rarely to almost non-existent, while the potentiality for misogyny in men is huge. I think it's because men and women are different, and it's more likely for men to objectify others.