Yes, I have a legitimate reason why they would be good for society.
No, i can't find a rational reason why they would be good for society.
They force governments to refuse corporate influence.
In Mexico, large portions of the country are run by the Cartels. They are apparently a great source of jobs and fill in many rolls that the government is unable to do, like various social programs. Mexico also made more money through illegal drug sales than it did from its largest exporting industry, oil. The Cartels have also bailed out Mexico's banking industry a few times and generally keeps them afloat and an estimated 20% of Mexico's GDP is based of the drug cartels. In many ways, they act as the defacto government for a lot of the local communities.