Parents absolutely hate my boyfriend

My parents hate my boyfriend and it's honestly fucking annoying hearing them talk about him. First, they don't like that he's from North Korea. He became a legal citizen before we even met so he doesn't neede for a green card. They ask me what was so wrong with his country that he couldn't have just stayed over there. He was talking to his parents over the phone one day and speaking Korean and my mom felt the need to tell him that we are in America, we speak American. His parents are still in Korea... So... They also don't like that he has autism. It never bothered me that he was autistic but my parents are saying I'm lowering my standards being with someone who is developmentally "Handicap". Their words not mine. They think I'm way to smart to be with someone autistic and my kids are gonna be 50% retarded. Again their word not mine. My boyfriend is plenty smart in my opinion. He's different but definitely one of the smartest people I know. They don't really like that he smokes weed either, but it's legal here recreationally and he doesn't even do it all the time. He tries so hard to be nice to them and get them to like him, but all they ever do is insult him and insinuate he's not good enough for me. They are my parents and I love them to death, but we've been together 5 years and are discussing getting married and I don't want this negatively in my life.