It's a surprise that Tinder launched Tinder Social just now in the US given that's the main source of the leaked data. Tinder Social was (and remains) opt-out in Australia while he was writing the article. Even if Tinder Social is now opt-in in the US, the fact they were dismissive of the vulnerability disclosure is concerning.

Any social network with deteriorating privacy is bad. One where the content can potentially be sensitive is even worse. If you started on a service and it kept becoming more private by default, that's fine - potentially annoying, but fine. If you start on a service and it kept becoming more public by default, then we have a problem.

The fact that Tinder don't realize Tinder profiles may contain sensitive information for a significant portion of their user base is hugely disturbing. As stated in the article, there are so many circumstances beyond cheating that this is still an issue.

Assume for a fictional argument that I was born into a religious family, "no sex before marriage" type of thing, but enjoyed one night stands. One might use Tinder to do so quietly. Tinder didn't allow your friends to see that information before - I assumed I was safe from judgement by my family and their friends. Then Tinder rips that privacy you thought you had away!

Saying that users should have known better is not an excuse. As developers we must operate under the assumption that best practices are likely going to be missed or misunderstood. Tinder violated that in an extreme way in an attempted land grab for a large social market beyond hook-ups and dating.

Disclosure: I'm friends with the author and commented on drafts.