Good grief that's awful. I don't understand the mentality of people who would do such a thing.
I carry a knife and have done since I was a teenager. I have had several over the years and never once have I thought of stabbing anyone with any of them.
I use it to open boxes and slit sellotape, dig holes for bulbs, cut wire, fish beads out of small holes in the pavement where my toddler has dropped them, pry the backs off watches, and a million other uses that I can't think of at the moment.
I am quite sure that if I was ever found with it on my person by a member of the police force I would be in big trouble, but I would quite frankly be lost without it after all this time.