While I believe that there might be some people who had no "morally" dubious intents, I fail to see why anyone with a traditional moral compass would sign up for this website.
Even if you are not married and simply looking for a one nighter, you are still signing up to site where married people are looking for an affair. It is right on their main landing page: "Life is too short, Have an affair". While it sucks for them, I feel it difficult to feel pity for them when signing up to a website which main intend is to make is to make it easy for people to cheat.
The other people could have simply signed up for a different website where the main intent is not cheating. It seems there would be plenty, and none of them are getting hacked