Morality tends to be governed by two views: you can either judge an action by its outcomes (consequentialism), or by its motivating principles (deontology).

From the consequentialist perspective, Walt's pretty clearly a bad guy: meth is a brutal drug with very little social upside. Sure he's able to bring about good for his family, but I'm sure there's a whole network of people who's lives are worse off because of his work. Overall he's probably created more bad than good in the world. Because meth tends to tear you down in the long run, I don't think it's fair to say he's responsible for the goodness of the high that his customers feel, as in the end it's a destructive addiction and not a recreation.

A fair response to this is that if Walt didn't cook the meth, someone else would, so there's the same amount of "bad" whether he does it or not, so why not take the money and run? I think the simple answer is that something doesn't magically become not-bad if someone else is willing to do it. Walt can still cook meth, but it's hard to say it's ethical from this first point of view.

From the deontological point of view, it's a bit murky. If you boil this down the view to its core, it's a moral test that's summarized as: "I can only do this if I'm ok with other people doing it too."

So, has Walt acted in ways that he (or we) would be alright with people doing broadly? Here's a couple spins on what he's doing:

1. "A man should be able to do whatever he needs to to provide for his family." While I might feel like I should be able to do whatever I need to to feed my wife and kids (provided they existed), I clearly wouldn't want someone else exploiting my family to feed theirs. So this fails the test and is immoral.

2. "I can profit off of goods that are addictive and destructive." This one is tricky, unless you're a libertarian and think that everyone is free to make their own good or bad decisions and that they own the consequences. I'm sure people will advocate this (and I assume the linked article will too, given the line "rational decision to provide a product to people whom have voluntarily decided to consume it") but I think it lacks nuance and legitimacy. Nonetheless, what Walt is doing would at least be internally consistent so long as he's okay with other people selling equally bad goods, and making them available to, for instance, his son. The argument here is the generic one about why stuff should be illegal or not.

So where does this leave us? I don't think there's a strong case to be made that Walt is a moral guy. No matter which of the two lenses we use, his actions look pretty bad. But I think that's what makes the character and the show so compelling: Our morals are an abstraction that we've placed upon the world to make it easier to navigate, and he's moved into a darker world where these rules don't matter, and what's more is that he's thriving.

I think that's the hook, that somehow this meek and mild guy who played by the rules his entire life was able to shed them entirely and find himself completely at home--and the audience is along for the ride, assuring themselves that they could thrive in a world without rules just as Walt has.