Anyone can mod anything. Someone can ruin a Mustang, Corvette, CBR600, a Ninja etc with crappy mods. It's all in the eye [or ear] of the beholder, so to speak. The good news is if you get a 750, the stock exhaust is quiet and civilized. You will certainly not disturb the peace with it. Exhaust being too loud was a concern for me, once I heard a stock 750 at the dealer I knew I would be fine and not upset my neighbors. A good exhaust, to me, is not something that is loud for the sake of being loud, but something that has a nice deep tone/note. The stock exhaust is OK on open throttle but lacks that at idle IMO which is why many switch. Some of the aftermarket exhausts are both loud and deep, some are quiet with a deeper tone. I may upgrade to the Harley Screamin' Eagle exhaust, since that also appears to be relatively quiet as delivered, but with a deeper tone.
To each their own.