There is an average of one autistic per classroom, and it commonly disrupts the learning environment. In recent years, I have seen many classrooms disrupted by kids with autism in the middle of an important lesson, sometimes even a test.
Autism is a serious condition that requires special attention and care. Why should we put them in the mainstream school? It would not be right to allow students with autism to be in the same classroom with other normal students. This would also cost lot of anxiety and stress to the autistic kids. Also, it would put too much pressure on teachers who are not specially trained to deal with autistic students and their needs.
Kids feel better by putting them in normal classes infringes upon the learning environment of those who actually learning something and have opportunities. Keeping autistics in the same school as normals, that for me is just going too far.
It is absolutely pointless! Those few kids scream a lot, give goofy looks to other kids (kind of creepy), and talk like a lunatic. They will get poor grades, as following directions may be hard for them, and will be bullied. They might commit suicide as a teen, because kids alienate them. Autistics are constantly provoked into lashing out/having a tantrum and teased by the other students and the others have to put up with constant disturbances and distractions in the classroom. I think it would be better for everybody concerned that children with autism are taught in different classrooms.
While others can behave very well, most kids will shun them, and even run away from them. This can have bad effects on them, if it continues. Clearly, it is bad for the child, and bad for the normal students.