People like Kirk Douglas and Gregory Peck, were big move stars and also of an egalitarian, humanist bent.
They promoted their ideals by choosing to do certain films and portray certain characters (eg. this, spartacus, to kill a mockingbird)
What can modern movie stars do though? When Hollywood just churns out tentpole blockbusters. Not much of a choice there.
Classic Hollywood knew how to do big franchises right. You did two sequels, then you sent off your protagonist to do a film where they meet Abbot and Costello. That was their Avengers.