First, not all otaku think that way --- actually its a rather small but very loud minority from what I can gather. I suppose you could argue that they're just very retro-conservative that way - a weird cultural flashback to extremely misogynistic times.
Another argument might be that the small faction that gets their undies all wadded up over the notion are also "untouched by women" and they hate the idea of their fantasy object having more experience than them.
Whatever, there's little reason not to skewer such nonsense when it crops up - whether it be abusive of 2D fictional women or real world seiyuu/idol women. It is fundamentally irrational and shows a distinct failure to connect the dots as you notice
