If that’s the case, then wouldn’t you find conservative judges voting as a bloc more often? Or are you saying that the ‘conservative’ judges are not conservative but actually all over the map?
I would interpret it this way: The ‘conservative’ judges try to follow the constitution, but they don’t always agree on the interpretation. John Roberta also seems to be protective of the court itself, and sometimes moves over to the ‘other side’ if he thinks a particular ruling would be damaging to the court itself, especially over contentious issues. That’s why he went over backwards to save Obamacare, much to the consternation of many Republicans.
An intersting statistic to dig up would be how many times each judge voted to uphold laws passed by the party of the President that appointed them, or to strike down laws the opposing party passed.
All that said, In researching this just now it’s pretty clear that the justices are a lot closer than most people think on most issues.
The page linked below shows both the political leanings of the justices, and also how they have voted in general categories deemed political. And there’s a huge divergence between them. For example, Breyer, Stevens, Sotomayor and Kagan are all clustered together as liberal, and the conservative justices are almost equally clustered as conservative. And yet, when you look at their votes, they are often very close to each other.
For example, on first amendment issues Stephen Breyer, a liberal justice, voted for the ‘liberal’ position 55.8% of the time, while John Roberts voted the ‘liberal’ side 50% of the time.
Samuel Alito, rated the most conservative judge, voted the ‘liberal’ side 39% of the time, while Sonia Sotomayor, rated the most liberal judge, took the ‘conservative’ position 32.3% of the time.
On federal taxes, all the justices vote the ‘liberal’ side more than 50% of the time, and surprisingly John Roberts and Samuel Alito have voted the ‘liberal’ side more often than Elena Kagen and Stephen Breyer.