US here.
I have bipolar and have been hospitalized numerous times. Each time in a mixed sex unit. I was/am young (18-22 when hospitalized.)
I was regularly sexually harassed by other male patients. I had men regularly try touching me, propositioning me for sex, and even trying to enter my room. Another young girl I shared a unit with had a male enter her room and get into bed with her before the staff even realized. I had a very ill schizophrenic man become violently enraged when I told him that in fact we were not childhood sweet hearts and had never met before that day. Men on the units will masturbate or urinate in the hallways. One man went into a rage in the hallway - screaming about how he hated women.
I have seen giant men, over 6 feet tall - easily weighing 300 pounds charge nurses and shatter door windows. These men will often take control of the dayroom's TV and bully and threaten anyone that challenges them.
The staff are often underpaid, underqualified, and wore thin. They become apathetic, easily. A lot of them are also intimidated by the larger men on the unit.
Of course, I have also seen women "act out." Especially the women going through drug withdrawal or psychotic breaks. However, in my experience they are significantly less sexually aggressive! Pair that with the fact most women in psychiatric hospitals have severe trauma from sexual assault and male violence and its a complete recipe for disaster.
For-profit psychiatric hospitals are the worst offenders with the lowest standard of care. (UHS - Universal Health Systems - is beyond awful! I have been hospitalized with them and have worked for them in their adolescent facilities. Avoid, avoid, avoid! They cause more trauma than help. In one case they put my young, sexually traumatized boys, all aged 8-12, in with the boys aged 13-15 who are documented sexual predators. One of my kids was forced to perform oral sex. Why mix the ages? Because they didn't have enough staff. Why no staff? Because the conditions were completely dangerous.)
Sorry for the long rant. I completely believe that all psychiatric facilities should be separated by age and sex for the safety of everyone involved. I have way too many horror stories from mixed sex and age units.