Ehhh, I probably shouldn't be wading into this. My thoughts aren't all that deep, and palimpsest and hautdesert are doing a great job of elucidating points I mostly agree with.
Then again, I got my own hands, so I may as well type with them.
The most obvious trait is usually gender, it's an issue with very little grey area: You have an innie or an outtie, and if you fall in-between you probably identify one way or the other (but that’s a rude topic to inquire on).
What gender comprises, culturally, is a far more complicated notion than the M or F tickbox, and even what gender is, physically, can better be viewed as a spectrum than an exclusive proposition, I think. That it seems so simple and straightforward to you is, perhaps, just the luck of your personal experience and genetics. I liked your explanation of the grey area with age, education and nationality, but I think to single out gender as the place where no such grey area exists exactly demonstrates why making assumptions on the basis of gender can be so problematic.
Reinforcing a stereotype is something done by members of the stereotyped class.
This statement just knocks the breath right out of me. I'm not sure even how to approach it without being incendiary. As I understand it, you're saying that if I hold a stereotype, then that's the fault (or perhaps responsibility?) of the people I'm stereotyping? Zuwha? How are other people responsible for my thoughts about them? And how is a group responsible for the opinion I hold about the individual for being a member of that group? I can't even restate this in a way I can wrap my brain around it. I'm sorry. Maybe if you give it another run, I'll get it.
If I thought that all geeks online are male, and met only male geeks online, the stereotype would be reinforced. If I thought that all single moms smoke cigarettes, and all the single moms I met smoke cigarettes, then the stereotypes would be reinforced.
Actually (disclaimer: I'm not an social anthropologist, but I do read about this stuff sometimes) I think the way it has been shown to work is thus :
You (and please, take this as "one", the generic you) think Mexicans are lazy.
You see Mexicans being lazy. This reaffirms your belief.
You encounter a Mexican who is not lazy.
You can't fit them into your pattern. You decide that you can continue to think of Mexicans as lazy, because most of them are, as you've already seen.
The trick is, every subsequent non-lazy Mexican you encounter, does
nothing to balance the scales. They are always the exception to the stereotype, and therefore need not be counted. In some cases, the non-lazy Mexican will not even be mentally acknowledged, because they don't fit the stereotype. Once you hold the stereotype, it can only be reinforced, and is much harder to dismiss than merely finding counter-examples.
(apologies to any Mexicans in the audience).
So, what if I met a geek online, and they never gave any clues about their gender, and their gender never became an issue, how would it matter if I thought of them as a man?
I would respectfully submit that if you're thinking of them as a man, then their gender (as you've presumed it) matters. Otherwise you would think of them as something else - human, maybe. Opponent. Friend. Conversant. Person. Irritating little twit. There are any number of non-gender specific ways to think about people.
I'm with Steve on the idealism of hoping people think of other people as people. I would never try to force someone into this mode, argue them into this mode, or legislate them into this mode.
I will not, however, accept the impossibility of it. Especially not based on the prevalence of stereotyping and making assumptions.
I don't care whether someone misapprehends my gender in an online community. I get plenty of real life face-to-face misapprehensions that bother (and affect) me to a greater degree. I am more bothered by the fact that someone needs to box me into "male" or "female" inside their head before they can interact with me or understand me. Course, it's their head, so all my bother is mine to shoulder, though given a forum like this, I'll feel free to express it.