I'd rather the police knew exactly what I was doing than just see a small part and assume it was something bad. It's not an ideal situation, but given the whole terrorism excuse, but I'd rather be watched and know that I couldn't be confused with someone who has malicious intent.
To expand a bit for international audiences: They got a prison sentence. During that sentence they were sectioned. Even if the sentence finishes they can still be held in hospital against their will, because hospital is for treatment, and not for punishment.
In theory there are protections. People have the right to have advocates and mental health act tribunals and etc etc, but as we've seen from a number of scandals[1] the protections are not nearly as strong as they need to be, especially for the private providers. And, weirdly, providers of medium secure forensic units tend to be private sector providers.
[1] People with severe Asperger's being detained for very long times because staff cause stress and anxiety which shows as aggression; the Cornwall Report (people with learning disorders being chained to beds) and Winterborne View (people with learning disabilities being trapped under chairs or left out in the cold or punched in the face); the CQC faking reports. etc.