First, let's consider the legal matter of consent. The facts establish that DJ, the man in question, was incapable of consent. He consistently tested as extremely cognitively impaired, and except for Stubblefield and a few other facilitated communication devotees, communicated with others only by squeals and body language. It is significant that at the trial, so far as I know, the defense did not call any neutral parties who knew DJ--- neighbors, members of his church, or people from his day program--- to testify about DJ's communicative or cognitive ability. If any such evidence had been available, the defense attorneys would have pounced on it.
The evidence about facilitated communication is so overwhelmingly negative that there is no reason to believe that what DJ 'said' via this technique is what DJ really said. It is telling that no one outside of Stubblefield's circle---her mother, and a few FC devotees---were able to generate any meaningful communication with FC, even though they tried. If FC is really facilitating communication by steadying the arm of the would-be communicator, then it wouldn't matter much to the communicator who the facilitator is---presumably a trained cat or specially designed machine would work just as well.
So the 'consent' and eagerness for intimacy that DJ 'communicated' to Stubblefield is the product of Stubblefield communicating with herself.
But suppose counterfactually that DJ really was communicating and did in fact express his desire and willingness to become sexually intimate with Stubblefield. This supposition would not erase significant moral concerns, which I turn to next.
On our counterfactual scenario, DJ, while an adult in years, has been socially isolated through his inability to speak or interact with others in a variety of venues. He has lived with his family his whole life, and has had limited contact with life outside his very limited circle of household, school, day program, church. He has never been able to choose where to go, whether to go, what to read or watch on tv, with whom to interact. He has things to say but no one to say them to. Now, on our counterfactual scenario, suddenly he can communicate, with the facilitation of Stubblefield. Of course, he would fall madly in love with her. She is his liberator. This would be a predictable form of transference. Stubblefield, but not DJ, would be in a position to recognize this. She, not DJ, would be in the position to see that there is a gross power imbalance between them, that she has the power conferred by her experience, knowledge of the world, and her role in DJ's life; DJ, however, is like a person newly liberated from a locked room, only now beginning to navigate the world, and just as vulnerable. To commence a sexual relationship at this time, even if DJ expressed his desire to, is to exploit his vulnerability, his lack of perspective and patience gained from experience to assess his own desires and choose which to act on. Stubblefield, a philosopher and disability rights activist, should have been hyper-acutely aware of how their relative positions would make an equal sexual relationship between them impossible.
Worse, as his primary facilitator, Stubblefield should have been aware of the responsibilities of that position. The relationship between facilitator and communicator is of necessity quite intimate, and for that reason, it is even more important to avoid sexualizing it, especially when the voice of the communicator is just emerging. Eroticizing the relationship makes it more emotionally labile and unstable, endangering this hard-won voice.
Stubblefield also should have recognized that valid consent requires the possibility of its withdrawal. With his sexual partner as his 'voice', it is less likely that DJ would have been able to 'voice' an end to the relationship.
So, in my view, Stubblefield crossed moral boundaries as well as legal ones. I believe that she didn't think through the former, but she should have. About the latter, she probably honestly believed that she and DJ had a mutual, loving relationship, and so was stunned when accused and convicted of sex assault. But her belief was delusive, and she, as well as DJ, was its victim.
Our criminal justice system will sentence Stubblefield to many long, pointless years in prison, something I foresee with a good deal of regret, not because she is special, but because she will join tens of thousands of other people behind bars for the simple reason that our society has not figured out a different, better way to handle criminal offenders.