The problem with stacking the SCOTUS with idealogues instead of balancing it a little closer to the realities of the electorate is that the risk looms large of losing credibility with the people. Power shifts from party to party in the other two branches as befits the tides of public opinion but the SCOTUS is supposed to take a longer arc than that, more independent of but not totally disconnected from contemporary values.
The court needs a couple of political activists on each end to fairly and actively represent the thinking of those groups as well as swing voters who will cross over if the argument warrants it. A SCOTUS that is so biased that it's just using a rubber stamp all the time isn't going to be credible with the people and will undermine the perception of the rule of law at all levels of the judiciary. .
So a Scalia gets replaced by a Scalia and a Ginsberg gets replaced by a Ginsberg.