You know what? I probably know as much about socialisation as you do. But I can tell you one thing that I do know..... is that in schools children are classed by their age group and forced to socialise with children for up to 6hrs in a day, do they get to choose who they have to sit next to all day or spend their lunch breaks with? Nope not really.... so how is that any different to homeschool kids socialising at a homeschool camp? or a homeschool park day? or a homeschool whatever?
I'm not sure I understand your question to be honest? I don't see why it's seen as such a big deal that children who are home schooled are disadvantaged in terms of socialisation? It's the biggest stigma associated to home schooling. I will try to find you this article I read once it might explain it better
Sorry for not being clearer. I'll try to explain again...... you're correct. At school they don't get to choose who sit next to in class. A lot of thought goes into arranging each desk so that they share with 3 other children who are on a similar level academically but not best friends with. Then in their PE and Arts rotations they work with children from other grades - once again chosen for them. At least once a week DS2 goes to the classroom with the autistic kids where he participates in group activities with them. Like most other schools in Australia the children come from a range of backgrounds - different cultures, different religions, different economic circumstances, different family shapes, different shaped minds, different ages, yada, yada.... as you say they are forced to negotiate and socialise with children who are very different to them.
As a homeschooler you can take them to homeschool camps but the demographic of homeschooling tends to be either religiously based (it's huge in the Muslim community) or middle class, 2 parent, white, families. It's easy to socialise with people from the same background as us but forging relationships with people who are unlike us is far more difficult. So....... how do you ensure your children spend a substantial amount of time with people that they have nothing/very little in common with?

I think that the reason that socialisation is the biggest stigma associated with home schooling is quite simple - if you can't work with people who are not like you and/or people you don't much like there is a good possibility that you will struggle to perform in your workplace and life in general.