As a parent, you certainly do get to demand that your kids speak and act in certain ways. You get to demand that they do their homework and a reasonable amount of household chores. You get to demand that they not hit or tease each other, or make fun of the neighbor kid with no friends. You get to demand that they not engage in damaging and unsafe behaviors like drinking, smoking, or building wings from coat hangers and an old sheet and attempting to fly off the roof. You get to demand that they not scream “You’re a fucking bitch and I HATE YOU!!!”
You might argue that all these things fall under the umbrella of “basic decent behavior” and you would be right. But I’ve seen kids fail in all these demands, and have in fact been the kid in question a fair number of times. (Never called my mom a bitch or screamed I hated her–she would have slapped the teeth right out of my head. Saw other people do it, though.) And when kids fail in these sorts of demands, there has to be something to nudge them back on the straight and narrow. One of the more effectual nudges is temporary removal of some privilege they enjoy. A toy, a tv, visiting privileges, a trip somewhere, maybe a bedroom door.