It is difficult annsixty particularly since so much of the community education classes was scrapped.
I used to teach literacy, numeracy and IT for the LEA. In the last few years we had ended up having groups of very mixed abilities. Students with special needs joined classes not aimed at them because there was no suitable class available. Lots of effort was put into making it possible for special needs students to join classes and it did require extra preparation with risk assessments, identifying aids, etc., but help was available to do this.
Fortunately the students in most of my classes had individual learning plans and once the basic barriers were overcome, the way we managed having special needs students in the group was having more volunteers in the class, usually on a one to one basis. Most of these students wanted to be in a class of all abilities and I'll be honest, to begin with a lot of the students without special needs were wary of the special needs students - basically because they had so little experience of being around people with disabilities. I remember one student with quadriplegia cerebral palsy in an IT class who was very independent, but he had quite a severe speech impediment. Fortunately he was a very social person and the other students soon learned to 'tune in' to his speech patterns. I learned so much from that group.
But to answer your question about where does it end, personally I think it depends on the type of group and who is paying for the class. If I was paying to attend a class with the expectation of learning something new, then I would have something to say if any group member disabled or not, was disrupting the class for any reason - especially if I was working towards a qualification.
If the class is free, then as far as I'm concerned the more integration is possible, the better. There's too much discomfort and uneasiness about being in the company of people different from yourself (I'm not just talking about disability here) and classes are a great way of overcoming this.
BUT there are balances to be managed in any group and it's the group leader's job to do that. Part of managing the group means being aware and listening to all the members.
Gets off soap box 