CONTEXT!
This guy in the comic? The one with the hat?
He's a recurring character within xkcd, and.....
....Personally, I see him as the textbook example of ENTP. Charming, ultimately may have a good intention, but often times have a limited, selective understanding of things that ultimately presented as something that validates his belief. And a lot of his actions throughout the strip have a trolling quality in it. I don't see why this one is different (meaning, I think regardless of the underlying values, he's trolling)
Also, second context:
That comic is rather old, I think; not that girls haven't been on the internet for long..but more like, the idea that "HEY! GIRLS EXIST ON THE INTERNET BEYOND YOUR MASTURBATORY PURPOSES, FUCKING DICKWAD!" is rather new as the internet goes more and more...mainstream and casual.
Third context:
xkcd is made within the circle of nerds; I'm going to guess this particular comic also assumes the community talked is something 'nerdy', and that assumption overlays with another (old, outdated, ultimately WRONG) assumption that "omg girls don't like nerdy things". Like, they aren't talking about make up forums...you know.
Now, with that in mind:
I would like to say the problem exists within a personal spectrum; apparently most people in XBox Live or other online gaming communities, have dealt with this "tits or gtfo" every now and then. As much as the speakers are immature brats, I'd think it also hurts the target to some extent. Then from what I'd heard, around 'nerdy' / 'geeky' communities, women are seen as second-class citizen; as in, what they know is more suspect than others just because they have a clitoris and not a scrotum. Then there are less harmful 'stereotypes'; "Oh you're a woman? That's surprising, I don't find HALO to be the type of games women like!"
So perhaps it's not an universal maxim, but it does exist, and it does exist in a significant way for some women out there.
but I don't think it's that bad...as the creator like to depict, or the character like to think / justify in doing what he's doing
nowadays, or even back then.