If you're going to bring it down to that kind of strange technicality then yes - those people are using it because it provides them value in whatever form.

It's not up to you to judge what that value is and whether you think it's good for them.

This is just playing games with microeconomic terms. However you choose to define "value", using heroin is self-destructive and usually (always?) irrational. If you choose to include that kind of behavior in your definition of value then the word loses most of its useful connotations.

No it doesn't - because that's the definition of "value". Anything beyond that is your subjective interpretation.

It absolutely does provide value. Many (ab)users of illegal substances use them to provide relief from the emotional pain of traumatic experiences or mental illnesses.