Yes and no. For sure, they are dangerous to hearing and can easily provoke bad reflexive reactions that bypass our evaluation.
But - where I live, good 80-90% of cyclists on the roads are absolutely mad a-holes, and I try desperately not using more appropriate words. Red light with all traffic stopped doesn't exist for them. Unfortunately they are part of road traffic on many places, even though some good additional cycling lanes appeared recently.
I've personally as pedestrian have been almost hit 2x by cyclist going above 30-40kmh who zoomed through crowd of pedestrian crossing without even touching breaks, on red light. He drove not further than say 5cm from me, felt quite powerful wind wave he generated. This can easily end up in me being dead or permanently crippled (wife worked at emergency and they had exactly same case few years ago, the 40 year old pedestrian hit by cyclist on red light came in full consciousness, was dead within 2 days).
If you have such a person doing very dangerous stuff, rather than quietly tolerating and enabling him/her, horn is way more appropriate if it can make a positive difference. And as a car driver I've seen so many cases like that. I've seen probably drunken cyclist trying to smash kick side mirrors of cars stuck in traffic jam.
Just to be clear, I talk about Switzerland here. But not places are created equal - Geneva in this case is literally on french border from 3 sides, has tons of french folks living in it and even much more commute daily for work there. Suffice to say, Geneva has absolutely horrible traffic of all types compared to rest of the country (plus also highest crime).
Bikes should be on dedicated lanes, if Dutch or Danes can do it and managed to put it into tightly built medieval cities, many others can too. Then all the power to you guys. But mixing with traffic where every cyclist is an hard-to-avoid obstacle, on very narrow roads, thats recipe for many unhappy participants and some bad situations. In US this should be easier since every city US road I've ever seen is absolutely massively wide, often equivalent of 2 lanes here.