IMHO some of this comes from the was the modern society has changed in the last 50 years.
Likewise, I think this has much to do with it. These days (here in the U.S.) we're seeing increasingly frequent acts of violence. Just this past week: two college campuses and the regrettable incident with the psychologist. It seems to me the general public has two stages of "alertness" to their surroundings: completely oblivious, or hyper-alert, with no in between. It's the latter that I think makes many folks edgy when they see displayed what they perceive to be a weapon of some sort.
Recently, I had just returned from an outing, and still had my black-scaled SAK OHT in my pocket. A box with the super-tough strapping tape needed to be opened, so I was going to use the OHT. A couple of folks visibly shrunk back when I retrieved it from my pocket, thanks I suppose to its slightly larger size and the unfamiliar (vs. the trademark red) color. Someone spotted the SAK red/white cross logo, and says, "Oh, is that a Swiss Army knife?" — then all was well.
Edit: Bill ... your post while I was typing — echoes some of what I said regarding the SAK.