We deal with Black bears here in Colorado pretty frequently, at least you do if you or your neighbors leave any trash outside. In my experience they run at the first sight of people and any noise gets them out of the area. Around Winter Park where I car camp on the weekends it is not uncommon to see a bear or two as well. I suppose using bear spray would be an option if you were charged but I would be pretty hard pressed to see these urban bears doing anything other then digging through trash and pooping on the deck.
The bears in Yosemite are probably pretty used to humans, and I would suspect the real danger there is humans following or cornering the bears, possibly to use the bear spray they read about online. I can see all kinds of folks car camping in their rental, enjoying the great outdoors, and over reacting at the sight of a black bear looking at them from out of the dumpster. Crap, I bet the rangers were getting calls about sprayed bears multiple times a day and in the Springtime, it was chemical warfare. It is more of a how do we live in harmony with the bears situation. Many of the folks here in Colorado don't even report black bears anymore because of the one strike policy.
Obviously, If I was way up in the Sangre De Cristo's and I came across a black bear I would not feel this way. But Yosemite is a long way away from wilderness and the animals in that park are almost tame. I support the ban.