Imagine for a moment that you have a seven-year-old son who broke his leg falling off a trampoline. As far as doctors can tell, it healed just fine, but he's continuing to limp. Reasonably, the doctor thinks that physical therapy would be good for your son.
You sign your son up for therapy (it's done when you're not in the room), and after a while, you notice something odd - your son's limp is gone in public, but gets worse at home. Not only that, but he will outright lie if anyone asks him about his previous injury - it was only a pulled muscle, he says. It didn't hurt that much, it's completely better now, he was never on a trampoline. You also notice that when he's in public, he never seems physically uncomfortable, but at home he frequently needs to ice his injury.
After asking your son some very pointed questions, you learn that his "physical therapy" hasn't been working on making his leg stronger at all - they had been teaching him how to hide the limp, and giving him a candy every time he did it well. They were also coaching him on how to lie about the injury, because they had realized that you were embarrassed that the injury happened in the first place (you had forgotten to remind him to close the door of the cover of the, trampoline, so you were having guilt), and this therapist thought that your comfort was more important than his. He hadn't wanted to lie, but he was denied snacks, bathroom breaks, and water in those long therapy sessions until he promised he would lie any time anyone asked him about what had happened.
The reason why he was hiding his limp in public but not at home was that he feared that other adults would scold him for limping too (the therapist had told him that people don't like children who limp), but home felt safer.
If all this happened, you'd be furious. This entire situation was incredibly abusive - was it not? Your son was taught to hide his pain - by any means necessary - at his own expense - just to make some other people more comfortable. And to what end? Some other people around him got to swallow a comforting lie that he was doing okay, and according to the therapist, that made everything they put your son through worth it?
This is exactly what ABA does - it trains children to hide their own discomfort - and whatever they're doing to manage that discomfort - from other people. Just to make other people somewhat more comfortable. It's not a child's fault if his autistic traits annoy some people any more than it would be his fault if someone decided that they didn't like to see a limp.
If you aren't okay with a "typical" kid being trained like a dog to hide his discomfort, why do you think it would ever be appropriate to train an autistic child to hide their discomfort, or their traits? That's beyond cruel.
If something's abusive to do to a "typical" child, it's abusive to do to a disabled one. If anything, behaving that way to a disabled child is even crueler.