Pictures dont make it the councils fault. I think the point the guys are raising is that doing parkour is asking for an accident, and you cannot expect the council to cover the cost of you acting like a lunatic this time. Will you ask the council to shell out compensation when the multi-story car park is 1 metre further away from the roof you where jumping to than you believed?
Owing to previous experience these guys are naturally concerned they're going to be paying not just your medical bills, but compensation for improper placement of a multistory carpark, and then paying your sick pay until you are back to sufficient health to work, before claiming invalidity benefit later in your life because your old injuries prevent you from bending over to shine shoes.
I came off my bike when I was young, it was a HUGE crash and i've the scars to prove it. The ambulances where on strike that week and I got taken to hospital in one of those army lorries, spread eagled over tank cutting equipment. The nearest A&E was on strike, and my parents where notified by a hastily written note on army paper stuffed through the letterbox (but not which hospital I was taken too which is a story in itself).
The accident was around 1990 or so and a few years back I went past the hedge that finaly arrested my not inconsiderable mommentum after 200 metres of skimming across the road surface and a kerb. You could still see that the section of it my flailing body had removed still hadn't fully recovered.
Should I have sued the council for making road surfaces hard, or for making hills steep, or for bushes having lots of thorns in?
I didn't sue them of course, I was back doing sports at school before the bandages where even removed - although they wouldnt let me do swimming. Then again I was already in considerable permanent pain anyway from an accident on a school sports pitch where the posts didn't have padding around them - maybe I should have sued them for that...
The irony of course, is my grandparents still think i'm a woos.
Kids today have no idea !
Now i'm not implying anything, merely explaining their concerns and telling a few stories. Maybe this is an opportunity for you to prove these guys wrong? Go do parkour, get yourself hurt, and then - reality check - don't sue anyone! That'll maybe restore their faith in you.