All points well taken. Nothing like a loud horn!
IMO, a good loud horn is a must have. And, don't hesitate to use it - gotta make sure [if you can] that they see you. Let's face it, guys, cages pull out on or turn left on other cages! Why would we riders think they will do differently on us? Watch that front tire - it'll show more movement than any other part of the cage - if they begin to move.
I blow the horn [got a loud one] every time I even SUSPECT they might come out. If it offends someone, who cares - I'm only interested in being seen and staying in one piece. If you even suspect you need the horn - blow it - every time. Hesitate and die! By the time you hesitate, they've got you!
Recently here, a sweet ol' lady let the first of two riders go by - then she pulled out in front of the second bike and killed the rider. If he had blown a horn [in time] chances are he would still be alive. Last mistake he ever got to make. I just assume they are all out to kill me. Ride with your thump on the button.
The jury is still out on loud pipes. Likely, Scrapvalue is right. And, with the windows up, air cond on, plus music - - - and cell phones!!!! Loud pipes do more to satisfy the rider than to increase safety. You'll either be right beside 'em or already past 'em before the hear the pipes.
This is just another FWIW, guys.
Let's all "be careful out there".