I don't think having a loud exhaust is bad. However if you abuse it by rev'in the engine as you drive thru some sleepy neighborhood at 2 in the morning...then you give everyone else with them a bad name...and you just want to show off...I personally don't care if someone wants to show off...just do it somewhere that doesn't bother anyone else...alos remember some people have night jobs...so they won't be too happy if you show off at noon either...
Cheers,
Robert