I'm going to do this in reverse of how you had it in your post.
No worries, the order was not important.
A) there is a big difference between "cant stand" and "wouldn't normally go out of your way to know". You get involve because you like the activity, and if you like it enough, you might learn a little about how to get on with those who are outside your normal comfort zone. I;m not even saying far outside your norm, just a little.
There certainly is a difference. However, that doesn't change the fact that every now and then you have to interact with both of those groups, at least to some extent. Be it a prospective bully, a boring neighbour or an intrusive classmate, you will run into situations like that. Then you indeed use social skills and thus develop them.
B) people DO make this judgement from afar, by colour, gender, other physical characteristics, clothing styles, et alli.
C) there was some group work in school, but as you go up in grade, it becomes less and less prevalent, and that's the time you're really starting to notice the differences in backgrounds between you and your peers. And when doing group-work with those outside your comfort zone it was done with a begrudging, uncomfortable silence. You do the work, you get it done, you don't talk beyond that, unless you would've talked to that person normally. I was in groups many times, but I was rarely in the group.
Certainly they make preliminary judgements like that, it cannot be avoided. However, consistently acquiring even remotely accurate and reliable profiles of people with no social interaction is not realistic.
We had groupworks pretty consitently throughout my school life until I started university where group projects are few and far between. Even if you are outside your comfort zone, you use your social abilities. Discussing the project, giving the floor to other members of the group, agreeing upon who does what and respecting the opinions of others are all social skills you utilise in those situations.
Actually, I was excellent at that. As was everyone else in my school. How many of the people in you school did you actually socialize with? How many of them could you actually have said you know what their goals were, how they felt about things? That is when socialization comes into play.
Our average class size was something like 20, slightly higher in high school (although most of the times different people had different classes, it was a weird system) and I usually knew where everyone lived, had an idea what their parents did for a living, and what their general interests were. The last category was hard to keep up with when we were younger, but in high school I knew those quite well too. I am pretty sure I know what every single one of my old high school classmates are still doing.
In any case, even in high school the group projects were common. Moreover, all manner of parties and hobbies pretty much forced me to interact with a lot of people towards whom I was indifferent. I suppose one reason for that is that even if you feel indifferent or worse about someone, it doesn't mean the feeling is mutual.
We probably ought to either drag the discussion out of this thread or just call it quits.
