So many possible ways to answer...
Yes, no fangs or claws. Probably because we evolved (or were created, if you prefer) as tool users. Doesn't help if you don't have (or are denied) the tools.
A knife is probably the most generalist, non-specialized tool ever created. That makes it the most generally useful tool ever created.
Because it probably enhances my chances of surviving the unexpected by fivefold or more.
Because these days our packaging is almost universally more durable than the product inside.
Because these days if you NEED a knife, no one else is likely to have one.
Because Leroy Jethro Gibbs says to! (Gibbs' Rule # 9, "Never go anywhere without a knife.", pretty enlightened for TV, actually).
Probably the real answer: because I was born a knife nut, and am never without one without feeling naked, helpless and vulnerable. Apparently my government increasingly wants me to feel naked, helpless and vulnerable. I wonder why that is?
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Yeah, I wear a tiny titanium 185-lumen LED flashlight around my neck on a dog-tag chain. The watches I wear most often have compasses as a function. Two tiny tools to create fire on the keychain...