I might forward it to a friend to ask if that's the girl he dated last week, without meaning to give him passwordless access to my account.

A good way to know if he is really your friend ;)

The email itself could be intercepted, could it not?

I guess when an adversary knows about the feature and uses some social engineering against the user?

In order to get access to their... OkCupid account? Not sure that I care.

Imagine https://www.wired.com/2017/01/grinder-lawsuit-spoofed-accoun..., without the spoofing.

You might care if you were married and using OKCupid to find a girlfriend.

You may say that getting exposed for trying to have an affair is a good thing, but that's a still a reason why someone may care how secure their OKCupid activity is.

Certain sexual behaviours are outlawed in certain nations. And may result in death or long incarceration times.

In other nations, it may not be strictly illegal, but is more than enough information that, if publicly released, would result in death threats and other social pressures.

Everyone's got something to hide somewhere.