The idea that courts can decide whether a law is legal or not based essentially on perceived motivations is dangerous and impractical.
Motives are taken into account all the time by courts for all sorts of reasons – criminal, civil, administrative, sanctions. Sometimes they get it wrong, I’m sure, but in cases like this, I’d say the evidence of illegal motivation has to be so ironclad that I’m not terribly concerned. I’m sure if the courts feel there’s any doubt at all about motivation, if there’s any sense at all that they’re dealing with perceived motivation rather than actual motivation, they would let the law stand. It would have to be the once-a-century unicorn case where some buffoon left around ample documentary evidence of illegal motivation for the courts to intervene.