Here's a list of all the prisons where I visited (some many times!) :-

Wormwood Scrubs
Parkhurst
The Mount (Hemel Hempstead)
Hollesley Bay
Norwich
Wayland
Highpoint (North and South)

Many of 'my' inmates were terrible recidivists. On visiting them again, I found they were so upset at being 'inside' once more. I often gently asked why they continued to offend if jail was so awful. The answer was nearly always drugs. Theft, robbery and burglary in order to buy Class A drugs.
Their womenfolk would trail up to visit them (I often gave them lifts in my car) and secreted drugs in their ... er.. body parts, and babies' nappies. Sniffer dogs and enforced nappy changes put a stop to some of this.
I always felt some degree of pity for all concerned, and tried not to judge. But one has to be practical and put in place security systems to prevent attacks, danger and further criminal activity inside and outside the prison building.
I just can't see how these measures could have any effect if the prisoners were outside in groups doing work.