[eviks]

But you do have security, this measure saves actual people in actual reality

> You cannot claim that just because some users are 'saved' as evidence that this is an effective security measure

Why not? Saving people from insecurities is almost by definition a measure of effectiveness

> you can make an objective decision on whether it is worth implementing.

You can't since the value factors in your "provable guarantees" and costs involved are subjective and also depend on the users' characteristics

[chii]

> this measure saves actual people in actual reality

no it doesn't. The claim is that by removing publicly leaked passwords, the user is prevented from having their logins stolen. But you didnt know if that password was going to be used for stealing - it's an assumption. You also dont know if private leaks are already being used, and is undetected.

It's the same type pf claim that the TSA (transport security authority) is saving people from terrorism.

[eviks]

> But you didnt know if that password was going to be used for stealing - it's an assumption

But you do know for a fact that these leaked passwords are used for stealing, so forcing a password change would prevent that, ergo, save some users from having their data stolen. Private leaks have no impact on this

[chii]

> you do know for a fact that these leaked passwords are used for stealing

no, the passwords are revealed, but it might not be used for stealing. And passwords that are stolen but not revealed publicly will continue.

My point is that the site will force an update, but the user's quota of inconvenience is used up - therefore, a more effective measure such as 2FA will be seen as unnecessary by the user, and thus, lower the user's security.

This is why the solution is to not spend the effort/cost on trying to detect password leaks. It is to make 2FA.