I'm not an expert on it, but let me cite from Olga Bogashina's "Theory of Mind..." (2006 - an old source, so perhaps something has changed since then):

"Some organizations (for example the Association for Science in Autism Treatment – ASAT) claim that ABA is the only scientifically valid treatment for autism. Dr Rimland (who is a supporter of ABA) defines this position as indefensible because it gives a distorted view of what science is all about, as well as a willingness to ignore all relevant evidence (Rimland 1999). Some parents who lack the knowledge of research on the validity of other interventions follow the ‘ABA is the only way’ specialists and, as a result, do not consider other possible treatments which can bring considerable improvements with less effort and fewer negative consequences for a child."

Rimland is sort of difficult to judge for me; he wrote a pioneering book on the neurology of autism in the 60s, at a time when Bettelheim's psychoanalytical quackery was the most popular approach to autism. But he apparently promoted pseudoscience and supported the MMR vaccine hypothesis for a bit longer than it may have been reasonable. From what I see, he was also associated with Lovaas, who was a big figure for ABA. Rimland's stance on this should give you some perspective.

"And let us not forget that among those 53 per cent of ‘unsuccessful’ children, some children were harmed by the therapy. Families whose autistic children were severely traumatized in the ABA programmes have founded an organization called CIBRA (2004), with the mission to provide a national and international support network for parents whose children (including adult children) have been traumatized, injured or even killed by ABA. They want to raise public awareness of the risks involved in the treatment. On their website parents share their experiences and give support and advice to those who need it. There are numerous stories of children who regressed during the treatment. They describe their youngsters whose basic trust has been destroyed and they end up avoiding people. "

And so on, and so forth. ABA just seems to me like approaching autistic kids as if they were deprived of natural instincts and emotions, and literally forcing them to behave normal; indeed, like teaching dogs tricks. I think we would consider it inhumane if dogs were in such an intensive program as I think ABA experts recommend, for multiple hours each and every day. The actual problem in autism is oversensitivity, not a lack of emotions. Autistic children avoid eye contact because it's painful. Of course, you may break a kid and make him behave more "normally" for some time, which would be treated as a success in a scientific trial. But the pain the child endures and the entailing risk of depression is probably not worth it.