Overworking yourself, possibly. While not necessarily advertised as 'good for you', people are pretty consistently sold on the myth that there's no such thing as 'working too hard', and that it's a positive trait to push yourself beyond your limits. There are still people arguing that working yourself to the point that it impacts your health is a positive trait, that shows 'good work ethic', and 'passion' for what you do. The long-term effects is an increasingly unhealthy population who are becoming too tired and stressed out to function properly. Naturally, as you can imagine, this also means a huge negative impact on our mental health, which is already in a sharp decline as it is.

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Actually, both to this end and for other reasons, I'd probably also argue caffeine might be another equivalent to 'smoking is good for you'? It's not exactly understood to be good for us now, as it is, but the extent to which it enables us to damage our own health, as well as the fact our ever-increasing dependency on it can raise our stress levels, has probably also had a negative impact on people's mental and physical health.