Why regulate?

What is the point of regulating anything, given the difference between theoretical regulation and its actual results?

 In the 120 samples labeled red snapper and bought for testing nationwide, for example, 28 different species of fish were found, including 17 that were not even in the snapper family, according to the study, which was released Thursday.

The study also contained surprises about where consumers were most likely to be misled — sushi bars topped the list in every city studied — while grocery stores were most likely to be selling fish honestly. Restaurants ranked in the middle.

Part of the problem, said the study’s chief author, Kimberly Warner, is that there are quite simply a lot of fish in the sea, and many of them look alike. Over all, the study found that about one-third of the 1,215 fish samples bought, from 2010 to 2012, were mislabeled. 

I understand why people like the idea of regulation.  But if it fails nearly one-third of the time, is it actually doing anything?  What would happen without all the expense and effort of government regulation, would everyone be eating cod-oil infused vegetables instead of fish instead of only one-third of the people getting the wrong fish?  Would anyone even notice if the SEC employees weren’t keeping their eagle eyes on internet pornthe markets?