All I'm saying is be careful what you wish for, yes he was stupid - but - and it's a big but, nobody was actually hurt (by luck or whatever).
Going down the path of deciding sentances for "what could have happened" would be
imho worrying.
I will draw comparisons with motoring offences, your average law abiding joe/joanna, paying tax, insurance all have access to something capable of more damage than a fire extinguisher. I'm trying to say, you can sit at home and comment on such outrageous behaviour but overlook your own driveway.
How would they feel if this practice happened with motoring offences? Perhaps it should?
Dangerous Driving
eg overtake with no chance of success, perhaps have a crash but 'luckily' nobody hurt.
Magistrates Court = level 5 fine (up to £5,000) and/or up to 6 months custody
Crown Court = unlimited fine and/or up to 2 years custody (endorse 3 to 11 points)
Death by Dangerous Driving
eg as above but somebody unfortunately dies.
1 to 14 years imprisonment, disqual min 2 years and pass extended test, obligatory endorsement
So, lob a fire extinguisher off the roof and don't hit anyone get 2.5 years (up to 5 years max) - yet drive upwards of 1 ton of metal with no regard for anyones safety and up to 2 years max?
*i'm in no way condoning his actions, he's a complete twonk, and I'm not pro/anti motoring offences.