A morality in which someone steals something from you, and then also incurs moral obligations on you to address their mental health issues, isn't really scalable. If you want to help him and go above and beyond, more power to you and my blessings upon you, but it is a bonus, not an obligation.
It took longer for a virtue signaller to show up on this post than I expected. I expect most of them reached my second sentence and noticed I already pointed out that you had the option of helping them if you like, just not an obligation.
So are you saying pretty words to make yourself feel better while trying to put me down, or do you actually go and seek out mentally ill people to help out on some regular basis? And given how grand your words are, I'm not going to be satisfied with merely giving some people a buck every so often.
I fully expect those are empty words. I am not impressed. You are not virtuous for saying them.
I'll repeat: It makes no moral sense for someone committing a crime against you to create obligations on you. It is a bonus above and beyond what you are obligated to if you help them.
There was no obligation to me, just an opportunity to help.
"Do unto others as you would have them do unto you," is a good secular rule as well as religious.
I believe we'd be better off as a society if more people simply helped, as best they can, when the situation presents itself.
But you're not obligated to help, in my view, or especially not to seek out opportunities to help.
I suppose I just don't see it as an imposed obligation, but a chance for charity, even a little bit.
As far as morality goes:
Theological: Failure to help is a sin of omission, as it violates the Golden Rule. (Christian version, but there are many other examples in the major religions.)
Political: Locking someone up with other criminals creates a greater cost to society than psychiatric treatment.
Secular: Unreciprocated generosity relieves suffering. It can also lead to an improvement in reputation.
We could discuss each moral foundation in detail, from St. Augustine to Singer if you'd like.
As for my personal experience with mental illness:
I was able to convinve my cousin, who was in full blown psychosis, to get to a hospital (way harder than it sounds.)
I spent most of my childhood helping to care for my uncle, both physically and mentally disabled.
Also, I do volunteer work regularly for the homeless, many if not most of whom are mentally ill, in my home city of Washington.
Answering your (perhaps rhetorical) question is hard without being there to see the actual guy.
Morality is situation specific, OP was there, perhaps if you were there you would have done the same.
There may have been other people whom most anyone would press charges apon.
Revenge is a dry & tasteless dish against some. Some deserve justice, some need only pity and help. Rehabilitation is logically better than punishment. One case is unlikely to alter overall deterrance. Thus each case should be judged on its merits.
Perhaps the guy's obvious disturbance was a ploy to fool the OP, luckily the cops could assit in this judgement with assesment.
This is the failure of Zero tolerance, when it produces obvious injustice. Equally this is the greatness of a judiciary who weight not only guilt but intent and circumstance.
The only bad or anti-social thing, is abrogating personal responsibility. Such as avoiding Jury Duty. Asimov's 1st law shows both an action or inaction that cause harm are equivalent.