I voted for Utility and Cool Factor, but it's definitely more than that for me, and I'm sure a lot of others will agree. It's all of the above, and then some. I work a job where I'm constantly cutting tape, cardboard, plastic, zipties, the works, I also walk to work at 4am and back home, so I need it for defense in case I have an "oh shit" moment and need to defend myself. Not just from people, but the neighborhood I live in has a troupe of feral cats that lives near my apartment complex, I'm not risking a potential attack without a weapon. All that, and knives are just cool, they're the reason I'm interested in metallurgy. I never knew there were so many types of steels and such, I always thought "steel was steel". Knives have taught me a level of respect for my tools that I didn't have before I started collecting and using them. I'm much more aware of my personal safety and the safety of others with a knife in my hand than I am with a "safety razor" that I'm given at work. And beyond all that, I've made friends through my knives, they're always interesting to some people and I've forged some lasting relationships that started with a blade. I can't be seen without at least one on my person anymore.