maybe cause i am a geoscientist but i kind of come down on the fathers side a bit - if, by pumping sewage into cracks, the nps increased the rockfall rate in Yos above its long term natural level- then they fucked up big time and they should stop, and if it takes a lawsuit to make them stop then so be it.
at the level of an individual event though its pretty hard to prove or disprove causation, and anyways when you climb you accept the risks. but this could be likened to someone trundling boulders down on you as you climb a mountain somewhere - rockfall is normal but a boulder trundled at you by a person is not normal risk.