Merriam-Webster: > capable of being physically or emotionally wounded
That can certainly be interpreted as a weakness. And it certainly is for things like vehicles, buildings, etc. But in the case of humans, vulnerability only means "weakness" when said human is perceived as an object, a means to an end, perhaps in a business transaction. The fact is that humans are in their most fundamental sense defined by the capacity to be physical and emotionally wounded. Therefore the term, being vulnerable, when used to describe a human attitude rather describes that person's expressed transparency to their innate humanness. As per this thread, more often men deny their vulnerability as if they cannot be emotionally wounded, which leads to a denial of their selves as a whole. Having the capacity to be emotionally wounded says absolutely nothing about somebody's emotional strengths and weaknesses, because we can all be equally wounded. Being vulnerable however potentially indicates a person's willingness to be transparent about their inner experience, namely their emotions, which can be anything from being overwhelmed to rage.
While I originally saw this discussion chain as you playing devil's advocate, I realize now you've done a good job helping reframe the scenario in a much better light. For most people (including myself), we don't separate emotional honesty from vulnerability because emotionally we _are_ vulnerable. Working towards a sense of self that is comfortable with emotional reviews that are as intense as a code reviews is something worth striving for.
Me saying that being vulnerable is a good thing is not the same thing as saying that addiction is a good thing. Addiction is what happens when we as a society can't talk about feeling vulnerable! That's the entire problem in a nutshell. The problem doesn't start with addiction, addiction is the self-medication people apply because they can't be vulnerable enough to talk about what's really hurting them inside.
When a person feels sad they should feel free to express this emotion (i.e. be vulnerable) instead of having to suppress it to live up to society's ideals about emotional expression.
It's different to having a norm for admission of weakness being a marker of strength due to the courage required in the act, similar to how it takes strength for an addict to admit they have a problem and go get help. You want to normalise talking to someone about your problems with a view to improving the situation. You don't necessarily want to recast addiction (a weakness that you wouldn't wish upon someone you love) as strength, as a roundabout measure to get people to talk about it more. That just seems liable to backfire.