I've definitely heard bikes approaching on the freeway so I don't buy the whole people don't actually hear you coming argument. And if I'm on the freeway and I can hear their engines under load at high RPM's I go ahead and assume they're cutting through lanes and approaching at a high rate of speed which is good to know because then I know to not go switching lanes of traffic until the bikes pass because I also like to drive my cars fast sometimes.... I'd hate to change lanes and run into/have a bike run into me because they were switching to the same lane when a vehicle blocked our ability to see each other. It definitely helps. I understand that people hate hearing "loud pipes save lives" (and loud exhaust in general) but how many of us like being told we need to be wearing full gear all the time? "That's like, your opinion, man" To each their own
I feel much more comfortable when I'm riding with my gf and I'm on my R6 so people can hear us. I get really nervous when she takes her bike to work on her own and is on I25 on that little 250cc bike that is virtually silent to cars. Ideally if you have a loud bike it's not your daily so maybe have a stock bike as well, or at least just be respectful when taking it out (avoid night riding, speeding/excessive revving around residential/populated areas...)