I think it is not contradictory to have two thoughts on this:
1. The thieves are responsible for their actions and should be properly punished.
2. The situation that has arisen is inevitable based on where we are as a society.
We live in a country of harsh inequalities, which is particularly evident in London where those who have nothing, and limited prospect of changing that by legitimate means, live cheek by jowl with the wealthy, some of whom conspicuously display their wealth in public. That situation breeds the kind of amoral, nihilistic individuals we saw in the programme. Human nature is such that in those circumstance a certain proportion of those who "have not" will decide to simply take from those who have.
The criminal justice regime, regardless of how stringent it is, will never alter the fundamentals of that.