IMO, what drives them nuts is Alito's established 15 year record as a Judge. They know for a fact he's the type of Justice that will not write law, and they are unable to prevent his ascendency to the Court.
We haven't had someone with this type of extensive record since Bork. History isn't playing out the way it did for Bork. Just as they aren't able to relive Watergate or Vietnam and it drives them nuts.
Roberts had a two year record that was pretty light in comparison in which they could "hope" he wasn't what they suspected, and he was replacing rehnquist.
This is the reason for the difference in their reactions to the two men.
For my part I'm happy with the placements. Chief Justices have to be "peace makers" among members. Attempt to broker Majority opinions. They are the face of the court to the public. IMO, Roberts suits that position better than anyone on the court. Whereas the rest of the Justices are free to write books, make speeches, and it is in that realm Alito has the potential to affect talks at the legal schools for up and coming jurists. To influence students to embrace a return to the constitution through his writings, rather then the concept of a living Constitution. This is what Scalia does with his writings.
"History isn't playing out the way it did for Bork."
That's because there was no internet. No blogosphere. No alternate media. No Freepers.