Can someone please explain red cards?

Recently I have been watching the World Cup like probably every person here. I don’t really watch soccer outside of this so I’m still a little confused about red cards. They seem to be on the same level as targeting in American football. You get ejected immediately and aren’t allowed to return. But in soccer you have to play down a man? Why can’t you put in your sub? Also why do they receive a 1 game suspension? Usually suspensions in American sports are reserved for actual crimes on the court/field like punching another player or something of the sorts. The punishment for a red card seems excessive in my opinion but I wanna know what you guys think.