I first saw this in the movie version, which featured Richard Burton chewing through the role of the psychiatrist, about 10 or 12 years ago.
I must say that after reading a version wherein the original staging is described, I can't help but feel the filmmakers made a major mistake trying to make the play "realistic" in its setting. I think the artificial staging quite helps the point, but anyway...
Equus is difficult but well worth reading if you want think about things most people don't want to think about - i.e. is there some social or societal root cause in the aberrant behaviour that seems to be more commonplace than ever.
I'm not sure I agree with Shaffer's conclusion as to the answer, but he's certainly provocative with his answer and with the entire plot. I'm sure this was even more audacious in early '70s Britain than it seemed to em in early 21st century Quebec or now, in slightly later 21st century Toronto. And really, what's the point of drama if it doesn't make us ask uncomfortable questions of ourselves and society?