I have been IP 3 times in my life (the most recent last November). I can honestly count on one hand the number of kind psych nurses I've had. The rest seemed to go out of their way to be mean. And I have always been a cooperative patient, so that wasn't the problem.
There is no job that's easy. I think being an employee in McDonald's is way harder than being a psych nurse, but look at the difference in pay and benefits.
To me, psych nurses have zero reason to be rotten to people who are already going through hell. There are plenty of other jobs if a psych nurse is burned out.