Or better yet, why not just take a bunch of gasoline and burn down the other Italian restaurant?   Why don't business owners do that?  Why do we assume that business owners are inclined to be crooked? It is rare that  business owners act intentionally malicious to their competition, but even the best intentioned business owners will have a customer who they have a legitimate and healthy disagreement with.  

You DO run the risk of being accountable, if you didn't eat there. 

I think that 'competitor-defamation' is some sort of a bogeyman that got invented for people who can't imagine there's someone who would disagree with them.  

Although please change my mind:  Have there been legitimate proven case of competitor defamation? You hear about companies going after customers all the time, but have they ever found out it was the competition? I'm actually quite curious.