The Parable of the River

The Parable of the River is that

"It's not enough to pull drowning victims out of the river; we need to walk back upstream and find out who's throwing them in."

But how snake-infested and pitfall-ridden does the path upstream need to be, to make it more productive to just stay downstream and keep on pulling the drowning people out?

And how can you tell if it's real productivity - would the upstream creatures quit pitching them in, if rescuers left the riverside?

(And are any drones available, for checking upstream?)