As I stated in some comment about the subject, it make sense for it to be an inside job. The demand (close the website) was kind of ridiculous for normal hackers. My conspiracy bias make me think the shareholder/CEO wanted to blackmail their user.
The reality may be more simple and dim: a former employee seeking revenge.
I'm looking forward for a former Google employee to dump everyone secret nasty search and email. It will be fun.
So he convinced me it's an inside job...but:
If that fails to convince you, then this must: In the first manifesto two names of male members were released. In describing one of them the perpetrator states the he "spitefully" joined Ashley Madison the day after Valentine's Day. Anyone who ever had a significant other knows that women rate Valentine's Day higher than Christmas, and men think so little of it that they have to remind each other the day is nearing. To call an act the day after Valentines Day "spiteful", is a thought that would enter few men's minds. If this does not convince you then you need to get out of the house more often.
So apparently no man has ever called a man a scumbag, and also men are unable to grasp that Valentine's Day is considered important by many people in romantic relationships? Those comments make no sense.