Even more to the point, Superman as a character and a franchise (of which Supergirl is a part/extension) has been actively politically progressive from day one, taking on domestic violence in his very first Golden Age story ("You're not fighting a woman now!"), and proceeding to defend mine workers against their corrupt and exploitative fat cat bosses ("The Blakely Mine Disaster"), tackle white supremacists (the radio series' classic KKK storyline), and face down a xenophobic mob ("Obviously none of you can be trusted with guns, so I'm going to take them away from you!" --
Superman and the Mole Men). Superman has been an "SJW" for decades before that nasty little bit of reactionary code was ever invented.
And then there's
this, from 1950 -- a lesson still sadly unlearned 67 years later, as everything about our recent election makes clear.
In short,
Supergirl's politics, and their open expression, are fully in keeping with the proud legacy of perhaps America's greatest pop culture icon.