The only time I will ever let either go is when they're heading straight for the mouth of a blue tongue or a duck.
I don't relish squashing them, but nature is a cold place, it's eat or be eaten most of the time. 'Mother' nature is just one of those warm and fuzzy terms behind which humans find some emotional shelter.
I once had a look at Buddhism as a belief system and while I feel it has more to offer that many other spiritual belief systems I couldn't get past some of the incongruities.
It's not OK to kill a fish, but it's OK to eat a fish that someone else had killed. Absurd.
On your second point I would argue that people who persist in believing in myth over fact, even when the fact is staring them in the face, cannot be considered to be emotionally 'well'.