Of all these, I'd either choose "destroy religion" as it is still harming people today or "make racism totally repulsive" to remove some reasons for irrational hatred and crimes (I thought it already was repulsive, though; I also don't agree with shooting racists on sight).
But really, if I had that kind of power I'd do something much more useful if I could. Like cure cancer, bring democracy and wealth to developing nations or even change the world as a whole to a Star Trek-like utopia (in regards to Earth that is) where people work for work's and community's sake and money did not exist anymore because people derive their satisfaction from good deeds and laudation instead of material gains.