I'm not about to read 450+ posts to make sure I don't repeat someone, but I'll put my 2¢ out there: in my current line of work, geophysical surveying, we end up in wilderness areas a lot. Most of the time, we just scare animals away if they get near our equipment. In Canada, they have what they affectionately call "bear bangers" -- firecrackers used to scare overly curious bears away from us.
However, the bottom line is, our equipment -- and more importantly, our lives -- are more valuable than any animal, regardless of cuteness or intelligence factor (or indeed, endangerment.) Some surveys see us carrying rifles -- for example, in regions where bears are just coming out of hibernation (read: they're hungry and in a foul mood.) If they get too aggressive, we shoot to kill. Also, story goes (so I hear), that some animals, like Polar Bears, are shot on sight. Those bears apparently go after their prey relentlessly and cannot be dissuaded by anything (firecrackers, rocks, shouting or whatever) so as a precaution they're taken down before they even think about going after a crew member. The principal is that it's a matter of safety.
For me, personally, I don't kill things. Sure, I've had my moments as a kid, catching mice around the house, but I generally just don't -- I usually don't have a reason to -- however I wouldn't hesitate if I actually did. I'm not about to judge others for doing so -- animals kill each other all the time, after all. The one thing I have a problem with is if people kill senselessly -- if someone kills an animal (read: deliberately, as in hunting), they should make use of the animal in some way and not be wasteful.