SCOTUS has no police or armies to enforce its edicts. The institution functions entirely on "trust capital." Every time it strikes down some democratically-instituted law, it uses up some of that trust capital. Sometimes, it must spend that capital. But doing it too often erodes faith in the institution, and ultimately, that is the only thing they have.

I'd argue that Citizens United is a great example of that in action. In my opinion, the Court got the law absolutely right in that case. But they used up a lot of trust capital in the process.