[erikerikson]

It may be harmless in some regards but in some social spheres it will be punished (e.g. kids bring punished for swearing at school) and in others the consequence of swearing will be silent exclusion (e.g. not being invited to meetings or asked to lead efforts).

Those seem like harms to many regardless of feelings about language restriction.

[Hizonner]

I swear like a your-favorite-stereotype. When my kid was maybe 4, I told her "I don't care if you talk like I do, but people will give you trouble for it". Probably with more detail than that; it's been years now.

She fully understood the point, right then. She also had no problem with other advice about how people would react to whatever.

She's 17 now. I actually don't think I've ever heard her utter a "swear word".

Kids, in general, have no problem with the idea of social context.