In reply to grubus: In my experience it unwilling rather than unable.
If you have a proper leader who is prepared to say "Sorry lads. I know we've been training and planning for this for months and have raised lots of money. It would be best if we postpone the trip." you're good. If you don't then this is the result.
School teachers in the 60s wouldn't have had that pressure. It would have been (like it is now): Travel to North Wales for the weekend, wake up Saturday, check weather forecast, assess group, pick a suitable walk.
H&S has little to do with it. Nowadays you do the same, it's just that there is more paperwork. People don't like paperwork so the easy thing to do is not go, and blame H&S rather than just do the paperwork.
I'm a great believer in "If you want to do something, you will, if you don't, you won't."