Imagine if we defined 'good language skills' as 'speaking English well'. A celebrated Swedish author, who writes compelling and interesting books but whose English is very poor, would be considered to have poor language skills. I hope everyone can see the problem with that. The same problem arises when we describe 'good social skills' in terms of ability to relate well to NTs.
I think there are two distinct sets of social skills. One is the ability to 'put yourself in another person's shoes' and imagine how you'd feel in their situation, and use that to decide how to treat them. This works well if the person you're interacting with is similar to you, not so well if they're quite different from you. Most NTs use this set of skills quite heavily, because most people they meet are similar enough for it to apply fairly well.
The second set of skills is the ability to set aside your own perspective and pay attention to the other person, to figure out what they're thinking and feeling by observation. This is more laborious and inconvenient, but it works with anyone, no matter how much they differ from you. Most NTs seldom get a chance to learn these skills, unless they travel to another culture, form a close bond with an animal (merely having a pet doesn't necessarily count), or befriend someone with a developmental disability.
For autistics, and for many other people described as having 'poor social skills', what's actually going on is quite different. They are different enough from most NTs that 'putting themselves in other people's shoes' frequently leads to the wrong response - such as a 10 year old regaling his classmates with facts about cockroach biology on the assumption that they'll find it just as fascinating as he does. With time and effort, they learn to stop putting themselves in other people's shoes, and instead use the second, harder set of social skills a lot.
I think both sets of skills are important. Being able to put yourself in someone else's shoes, when appropriate, results in a far deeper experience of empathy for that person, and gives you a very rich knowledge base to interact with them. And though it's easier than the second set of skills, it does take a certain degree of self-understanding to be able to match up someone else's experience to your own and figure out what would have been helpful to you in that situation.
And the second set of skills is important in understanding diversity, in seeing the rich variety of experience for what it is. It's also, I think, important for social scientists, who use similar strategies even when dealing with their own 'kind' of people. And it's important because even NTs can't always avoid interacting with people who are different from them. You may find that circumstances throw you unexpectedly into a situation of bridging difference, such as when a new mother is told that her child has a developmental disability.
Atypical kids often learn the second set but not the first set. This means that they learn to see interaction in general as difficult and confusing. It also means that they have more trouble developing self-understanding, because they don't get to form links between their own experience and what they see in others. Alexithymia, the inability to name or identify your own emotions, is commonly associated with autism. I suspect most kids learn to label emotions by having adults correctly recognize and label their own emotions as they're feeling them (which is harder when the adults are struggling to bridge a difference between themselves and the child), and by empathizing with others while hearing people label the others' emotions (which is harder when you wouldn't feel that way in that situation). Spending time with people who are 'like you' is very important to understanding yourself.
Which brings me to the topic of integration vs segregation. Atypical kids, in order to succeed in life, need to learn skills for relating to NTs. And segregation is often used as a way to deny a proper education and enable discriminatory practices - no 'proper people' see it who aren't participating in it, and the children don't see counter-examples to make them question it. But on the other hand, segregated spaces are important, since they allow atypical people to connect with others who are more similar to them. The solution, I think, is to allow opportunities for both integration and segregation, and to make sure the segregated spaces are voluntary and positive (and preferably organized by the same kind of people who participate in that setting, like Autreat).
Neurotypical people often miss out on learning the second set of skills. Being the majority group, this only causes problems under special circumstances, but it does mean missing out on some of the richness of human diversity. And it can be a serious problem for atypical people, dealing with a society where almost no one knows how to relate to them. Furthermore, as I noted before, NTs can't always tell when they'll be thrust into a situation requiring the ability to understand someone very different from themselves.
And here is one of the best agruments for integration - when it's done well, it gives NT children an opportunity to get to know someone different from most people, and to develop the skills to understand them. That is, when it's done well. Many times, atypical kids in typical settings are rejected. No one tries to understand them or see their point of view. Instead, they learn that in order to be accepted by the people who matter, they must distance themselves from anyone who doesn't fit in. I don't think my classmates in any of my classes learnt anything valuable about relating to autistics kids from knowing me, for example.
Other opportunities are cross-cultural encounters such as exchange programs or simply having immigrants in their social group. Being an immigrant, of course, is a potent way to learn about difference - I remember reading about a father of a high-functioning autistic boy who gained a better understanding of his son after they moved from US to England and he started running into social misunderstandings. Having pets can also be a good experience, but only if you approach your relationship to them with the understanding that they have their own, rich, nonhuman experience of the world. If you anthropomorphize them or else treat them like objects that happen to move around on their own, you won't gain much in the way of understanding differences.