Or maybe he thought it was compassion. After years of rehabilitation and finally accepting that she would never get better, he knew she wouldn't have wanted to live that way and it was the last thing he could do for her. Now, I'm not saying you have to agree with that, or even understand it, but it's just as valid of an explanation as "just plain meanness."
Many people have expressed feelings similar to that explanation.
Where are her the ashes Hildy?