That's really what makes this show special; demonstrating how the "noble" (if you want to call it that) intentions of Walt have been smashed to pieces by his own ego.
... The road to Hell is paved with good intentions
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And yes - I agree with pretty much everything you have said
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It's fairly clear that, this season, he has crossed that line. He didn't *need* to keep cooking meth, but he chose to. In series 4 he was very much under Gus's thumb, and trying to escape with his life, so it's a little easier to forgive his "sins". But if we go a little further back, he wasn't forced to take up Gus' super-lab offer (though unbeknownst to him it saved his life from "the twins"), and he did so largely to spite Jesse who was branching out on his own with the blue meth.
That's another thing I like about the show - it's so morally ambiguous that it's difficult to pull out all the threads, even with the benefit of careful hindsight.