Natural history dilemma

I spend a lot of time observing the ins and outs of natural history, so I often run into a species of moral dilemma: do I intervene, or do I just watch and document what I'm seeing? Sometimes, there's a clear right answer. For example, if I spot a turtle trying to cross the road, I almost always attempt to stop traffic and help the reptile reach safety. In fact, as long as it's not a Snapping Turtle, which is likely to try to bite the hand... or foot... of the intervenor, I'll even pick up the critter and carry it across the street. (With a snapper, I use a long branch to prod the turtle to move in the right direction.) But this situation is less clear-cut. Were this a ghost web—a construction left in place by an absent spider—I'd have probably freed the hapless Spreadwing Damselfly. I hate waste, but, of course, the ode would eventually feed the decomposer community. However, the spider was tending its web and had already delivered a lethal dose of toxins into its next meal. The predator had even started packaging dinner. There was nothing more I could do, save to bear witness.