It is when the Bill of Rights is clearly being trashed, and when their decision does nothing but further muddy the waters...waters that were already muddy enough because of the Court.
In the long term, a philisophy of deciding only what you have to decide to reach the decision is a proper judicial approach. I agree with you that some precedents from the past 40 years of excess (like McConnell) "just need killin'." They will be killed eventually. But the court is going to go at it one step at a time.
I am very pleased with this decision. Were we ever to get one more real conservative on the Court, this would go down as one of the great Supreme Courts in history.