I don't think it's stupid, but humans who have more sensory input (noise) will hear you (and thus notice you) in more situations if you have a decent sound-signature than if you don't.
In essence, there's a very good reason why artificial noise-makers have been added to electric vehicles, or why trucks are designed to beep when backing up.
Granted, it won't work in all situations, but it will help in many.
As Cruizin' wrote, you should still assume cagers do *not* see you, just as it's safer to assume the shadow in the bush is a tiger than to assume it's not, because one assumption keeps you safer than the other.
But, people still make noise to scare-off bears when tramping through the woods so they don't surprise one and get attacked.
The same principle holds true with noise on our bikes. It's no guarantee, but it helps. A horn is no guarantee (Stebel Nautilus or not) but it certainly helps, and moreso from the front where our bikes don't naturally have a good way of generating sound waves that go that direction apart from a quality horn.
There will be non-ideal locations where people won't hear your exhaust or your horn, as sound is omni-directional but it generates stronger pressure waves to one's eardrum as if there's no interference or if we're in an ideal location in front of the source. You can hear a Marshall stack from behind (with noise coming through) but one can hear it much better from the front. As we run around the stack we can still hear it in varying levels relative to the pressure waves and our ears. In fact, that also tells us where this noise is relative to us.
So, with a bike that has a decently-noticeable exhaust, you simply will hear it more-easily than one that is very quiet. There's going to be diminishing returns here, and it's possible to have a bike so loud that it simply angers everyone around you, making potential road-rage where one was simply trying to be noticed. A 'reasonably' loud exhaust would be the compromise I look for, and have found, with my Yosh baffle-in full exhaust.
Even when I am cruising around in my rorty-sounding FIAT 500 Abarth—dozy and/or distracted cagers get an earful if they don't pay attention...and they notice me. Inattentive pedestrians get a little blip just so they know I am there...or people backing out of spots blindly might hear me as well. One person who was situationally-oblivious had her door-open, blocking a prime parking space. A little blip from the engine got her off the phone and closing her door. I was also concerned that she was going to close her door when I was in a position for her to hit my car or worse, she wouldn't be able to close it at all. She had no concept of what was happening around her. The sound of my blipping engine woke her RIGHT up.
Most people can hear, and so sound will always be effective at signaling one's presence. This should not be confused with best-practices as it pertains to surviving one's ride. Hi-Viz gear might help one be seen, but few would assume that one should rely on this, utterly, for 'protection' as cagers notice us and no longer pose a threat. The exact same argument applies to a reasonable sound-level.
