You tried beeping your horn at pedestrians on country lanes who havent heard you come up behind them? You get abuse.
Plus not advised if they are on a horse either.
but they ought to be a button to make a louder engine sound to make you more noticeable to pedestrians
I have, on occasion, yes - obviously not a loud blast, just a gentle pip to warn them if they seemingly haven't spotted me. Not suffered abuse so far, I think it's always been obvious that I'm doing it for their benefit.
But I will admit, I was being a bit impish with my response

- I do actually agree in principle, at slow speed, an electric car can be hard to detect until the last moment.
It's not an insurmountable problem though. I was on a trip in Italy a couple of years ago, and noticed in Florence that all the of the taxis, which were largely BEVs or hybrids, would emit a constant beeping noise at slow speeds. It wasn't annoying or intrusive, like the reverse beep of a lorry. Just roughly loud enough to equate roughly to the volume of an idling engine. Surprisingly useful, especially in tight medieval city centres with lots of tourists on foot wandering around. Of course, once they are above about 15-20MPH, they become no quieter than an ICE vehicle, due to tyre noise.
And you are of course right about horses. I always call out to the rider to warn them I'm about to pass if I'm cycling, so I don't blast past them and freak out the horse. But I can see how a silent EV might be an issue.