I think you're jumping the gun a bit - you will get to experience a wide variety of nursing roles when in school, which will help you find where your interests really are. And the great thing about nursing is that you aren't typecast - you can work in psych for a while, work in oncology, ICU, L&D, and so on. Heck, you can work more than one job at a time, too.
Psych isn't all about therapy and touchy-feely stuff. It's about keeping your patients safe when they can't (or don't want to) do it for themselves. Depending on the setting, it's highly physical, and you definitely give your share of injections and get splashed withenough bodily fluids. I've been spat on, (intentionally) bled on, vomited, urinated, and **** upon, had used feminine products thrown at me - washed my hair at work more times than I can count! And don't forget the death threats and insults upon one's person. But I wouldn't trade psych nursing for anything, because I really love this population.
Don't put too much stock in personal experience, either - many psych professionals have their own battles, but this isn't always positively translated into good patient care. As I'm sure you know from your current degree, psych professionals have to be very self-aware, and to be on guard about how our personal experiences are affecting how we view our patients (transference, etc). Thick skin is crucial in any nursing role, but especially in psych.
What do you mean by not being able to volunteer in the hospital as a psych nurse? RNs are RNs - we're just specialized, but are fully qualified to do anything another RN can do.