Humans will to some degree ALWAYS give preferential treatment of some sort to their own tribe.
I fully agree. I only claim that we do have some power over
how we define those tribes. For technical discussions on the net, and for engineering/science work in general, (hobby) interests and experience makes for a much better glue for a "tribe".
Like Big Clive says in his Saturday Lives, "Hello to my technical family."
He has pointed out a couple of times that he knows quite a few technical people who aren't heterosexual. I don't think it is a coincidence: I think that because technical people are more interested in technical things than social details, it is much easier for all kinds of persons to fit in. It does not matter how "weird" you are; as long as you do good work and help others you're accepted, because those social details are just details, a spice if you will, and nothing relevant to whether or not one is considered a member of "the technical tribe".
(And, if I am correct on this, it means that "inclusivity efforts" in engineering/science fields, from programming projects to electrical engineering, will backfire: they impose new behavioural norms and patterns where individual variety was widely accepted, and therefore just end up excluding people. This has already happened, StackExchange network probably being the best example.)
For social networking like Fakebook, Twatter, etc., I have no idea or comments, since I do not use those.