Have a second kid only because you want to raise another child. A second child isn’t a loyal little puppy you get as a playmate for your first kid, it’s a fully fledged person with their own needs and wants who will have their own relationship dynamic with your first kid. I know very few adults who have really close, deeply meaningful “companion for life” type relationships with siblings. (“We like each other fine but aren’t super close” is much more common.) Siblings do play together as kids, but they also fight like cats and dogs, which creates a different type of work for parents. Kids also need individual attention. Two kids means twice as much time given over to it. It is definitely not less work (or stress, or noise, or cost, or responsibility) for you as a parent, and moreover you are under no obligation to constantly entertain your kid(s). I don’t play with my only child more than I would play with two children.