There are a couple of threads within this, err, thread.
One is about the ease (or otherwise) of SP moving into civilian jobs; the other is the issue of ex SP allegedly over-represented in Prison and homeless populations.
Let's look at the the first issue. Most ex SP quite happily manage the transition to civilian employment; additionally the transition assistance these days is pretty good - and flexible (unless you have the misfortune of serving in Germany). Furthermore, SP leaving are not some monolithic block of ex-Council Estate semi-literate 'Squaddies'. This bloc ranges from young soldiers just in their 20s to very senior, very experienced people, perhaps touching 60. No other industry would consider this as one target population.
On the second point of prison and homeless populations (and I have posted similar comments here before). I had a long chat with a very senior executive of a well-known Service charity, a year or two ago, about this issue. He believed that the figures were grossly inflated, due to a degree of opportunism. It is apparent that claiming to be ex-SP garners a degree of sympathy and support that one wouldn't receive if they were, say, ex truck drivers. Many of the homeless cases who claim to be ex SP are - perhaps a brief time in the TA, perhaps never completed basic training or left because of discipline or suitability issues. Same amongst the prison population, apparently.
That's not denying that there may be an issue and again, overwhelmingly, those who are legitimately ex Forces are overwhelmingly ex Army. Statistically this is likely; statistically, given the background of many of these people is that they are more likely to end up in prison if they had not been in the Army. I'm not saying that's right - it isn't, but it is a fact.
Again, if you come from a disrupted family background, with low familial expectations, poor performance at school, perhaps a history of petty crime and drug-taking before enlisting (accepted by recruiters these days) perhaps it isn't surprising that some - only some - might turn to criminal enterprise when they leave the Army. We should celebrate the social mobility that a career in the Forces offers. I can't think of any other career field that can offer such opportunities.