As others have said, wearing Hi Viz does not make you immune to morons, but it doesn't cure everything. As dorky as some may think it looks, there was a drastic reduction in the number of left-turners and people pulling out in front of me when I did switch to the Hi Viz from cool stealth black, but as I said, it doesn't cure everything...I've got an 18" titanium rod and a bone graft in my left leg to prove it. The driver of the truck did not see me despite a Hi Viz Kilimanjaro and helmet.
The key thing though is that it is another tool. Riding a bike is inherently dangerous...we all know this despite what others say, and it is your job as a rider to evaluate that risk, and if you choose, mitigate the risk with the tools available to you. To some, they are perfectly comfortable with the risk associated with riding completely unprotected. For others, they may need to dress up like a high viz Michelin man in a before throwing a leg over. Most of us are in the middle. As I'm already wearing at-least a jacket and helmet when I ride, choosing something very visible that will reduce (but not eliminate) the risk of me not making it home makes perfect sense.