Yeah, I wish people would quit using "ad hominem", it's turning into a tell for "people who spend too much time online and still don't know how to disagree".
Still, I think you're really overstating the risk here. The data set doesn't have email addresses and it doesn't list the specific services involved. How would you propose causing real harm to these real people using the data here, in a way that hasn't already been done or tried?
It sounds like he did put a lot of thought in to his decision. You seem to be arguing that he thought about it, and then decided to do it anyway to help his book sales, which would make him a pretty indecent person. Do you really want your opinion to boil down to, "I think this guy is greedy and bad"?
As far as the value of research goes ... well, we don't really know yet. This particular dump, yeah, probably won't add much value to the current body of research. (I personally have much larger dumps, and don't consider myself a researcher ... so it's not like there's a shortage of data available.)
That's the thing about research though. You start off by investigating something and seeing where it leads. Maybe this will be the dump that would encourage developers to start maintaining password blacklists ("Please do not use this password, it is too common"), that would be valuable. Maybe this will just be another straw on the camel's back that eventually leads to everybody giving up on the idea of passwords entirely.
Who knows? It might be valuable, it might not, but it's not dangerous.
