It doesn't matter the theory driving his votes, it matters the outcome. If you vote against say, civil rights, because you have some super-nuanced view about how the court can or can not be involved in respect to state politics, you're still propping up Jim Crow laws.
Read up on Baker v Carr which touched on the issue of redistricting. Specifically on whether the court could intervene in a state perogative case. On one side were a set of justices who believed that the court couldn't since they would be interfering in state matters. On the other side were justices who believed the court was the only possible body who could restore the voting power of minorities.
Strong first principles are great when we're arguing philosophy but it's pretty bad when we're preventing millions from exercising a fundamental right. The soldier who carries out atrocities because he believes in the duty of following orders is no less guilty of the atrocity.
This doesn't mean that the end justifies the means but it means that we must judge our course of action and the actions of others with their full weight, not only intention or goal but the direct cost too.
The road to hell is paved with good intentions.