Stable Diffusion allows for just about everything, including pornographic images and parodies of Xi Jingping.
MidJourney is a more controlled platform that doesn't allow for those things. And, because it's so tightly controlled, it hasn't degenerated into a mere parade of sexualized anime characters -- and it minimizes the political risk to its platform. MidJourney actually seems competently managed, in all seriousness...
Yes exactly. You or I may not like where MidJourney draws the line on allowable content, but if they want to run a service buisness they must draw a line somewhere.