First of all, you are talking about special needs students as if they are intentionally bringing back the class, but having a disability isn't a choice that's made. It is something you are born with.
Secondly, someone with special needs isn't more or less intelligent than a Nero-typical (normal) student, it just means that they have a different way of learning. Take Albert Einstein for example, because he was on the spectrum, Leonardo Devinci who was known to have dyslexia, and Walt Disney even had some disabilities (http://www.Disabled-world.Com/artman/publish/article_0060.Shtml)
One of the issues with teaching today is that there are plenty of resources out there for students with learning disabilities, but there are teachers and students who fail to utilize them, such as the Special Education Department which is becoming available in more and more schools.(http://www.Educationworld.Com/a_curr/columnists/mcdonald/mcdonald022.Shtml)
Part of the problem of putting disabled students in separate schools is that it may provide them with the support needed, but they feel separated from the other students, which does impact them psychologically. This may be my opinion, but it is backed by my personal experience as a student on the spectrum.
PS. If you are questioning my argument, bear in mind that I also made it into college.
Students with mild social disabilities, or people with mental illness should attend regular schools/classes. This will help them and improve their condition. Children with severe intellectual disability ( the ones that cant spell there names/basic words, cant count or do basic addition and are unable/ barely able to communicate) should not be allowed in regular schools. Retarded students disadvantage the students that can actually learn and have a successful life because they slow down the rest of the class, distract other students and more money is wasted by supporting them, when it could be used by the students that are more likely to get a good education/job and will ultimately have to support the disabled.