Where is the line between engineering for addiction and engineering for a quality user experience? Everything we are told about building modern services is abo

Where is the line between engineering for addiction and engineering for a quality user experience? Everything we are told about building modern services is about optimisation. You have metrics, you experiment, you tweak things, you see what helps and what doesn't. This is as true for business models as it is for interface design. Some of this is good - it is positive to improve your UI to reduce friction and make it more usable by your customers. Some of it is fine - choosing a landing page design that gets more people to sign up. Some of it is bad - things you do that mean people don't close the app as readily. All these changes are the result of the same process, that is built into how modern businesses operate. How do you draw the line between optimising for good UI and optimising for addiction? If you're writing legislation, do you outlaw specific practices? If you're trying to operate companies ethically, do you just avoid certain metrics?