> I'm not a cyclist, but I'm a huge fan of having these on bikes. They've become more popular in my area and because of that you notice the bicycles earlier so you have a much smaller chance of accidentally hitting them because you don't see them. After I started seeing these, I've become quite baffled why more cyclists don't use them.
I find the sentiment in your first paragraph to be baffling, though common. The problem isn't that horns (or high viz, helmets, or flashing lights) are a bad idea, or that you're wishing that more people would use them - I agree that more should use them. My issue is that the sentiment displaces responsibility on to the cyclist, from the person operating the dangerous machine. It's up to the cyclist to decide what gear works for them, and the burden of responsibility is firmly on the driver to not hit other people using the road.
It seems like every couple weeks, our local paper runs an article on another driver running in to a cyclist, and it nearly always frames the event as "cyclist hit by car" (notice we're already biased - "other-class-of-person hit by machine"), then proceeds to answer the "was the cyclist wearing high viz?". This creates a situation where it's more acceptable to drive carelessly, so long as the victim isn't following your locale's particular safety checklist.
Remember that there are a bunch of reasons people bike, and a lot of them are counter to some of these recommended safety products; people don't want to mess up their hair for work, have to wear a dark school uniform, can't afford lights, haven't considered any of this stuff, don't have a safe cycle lane to use...