Supreme Corp overturns SC racial gerrymander ruling

The lower court ruled that the gerrymandered map was based on race. SCOTUS said it was not (even though it was) and that it was just based on a political gerrymander. 

But why TF is gerrymandering based on political party allegiance legal in the first place? This ABA article explains that corrupt SCOTUS determination "based solely on the highly debatable suggestion that it is just too difficult to establish standards for separating lawful from unlawful conduct."

I wonder if the Corp will use that same rationalization in the immunity case? Can we really determine if trying to overturn an election is 'unlawful'?