well, i'll put it this way, loud pipes certainly don't DIMINISH your noticeability. and honestly, most motorcyclists like loud pipes. louder than stock at least. i think the beef comes from the fact that the absolute loudest bikes on the street are harleys. i live right near van ness and there are packs of roving harleys that seriously sound like a thunderstorm is hovering over your right eyelid
of course not all harleys are loud and the renegades i had on my falco and the yosh can i have on my zrx are far from "quiet". but i've never been offended by the loudness of bikes other than harleys. and that has nothing to do with whether i like the sound or not because i do like medium loud harleys.
they definitely don't do a whole lot of good for noticeability though. the sound is, first off, coming out in a direction where the people who notice it are of the least threat. and second, the sound is kinda non-directional.
but, hey, almost all of us like loud pipes.