Why on this good green Earth are you arguing about alignment in a thread about an adventure for a game that has largely eliminated the relevance of alignment?
I haven't been involved in any argument about alignment myself, but in defense of those that have (on both sides), I think its origins lie in the natural surprise (whether we like this aspect of the adventure book or not, I think it's a bit of a surprise) that a book about heists took the time to create a way to make sure that the participating PCs are not only allowed, but encouraged, to be good.
The purest, "by-the-book" following of the adventure keeps the characters in a very heroic light. I don't think that is all that surprising in itself (for one, it staves off any of the old "D&D's corruptive influences" arguments) but I think it still came as a bit of a shock that the reasons for ALL the heists in the books start from a heroic position.
Obviously (to me, at least), it would be easy enough to play it grayer. Honestly, it's probably harder to add goodness in than it is to take it out, so I understand why they may have chosen to write it this way.