Why not say that the policy is non-coercion except on important issues?

That’s like saying: “The police force should respect human rights except on important issues”. I’d rather say “let’s have a police force whose ethos embodies respect for human rights”—and know that there will be some failures to respect human rights—than have an ethos which embodies systematic disregard for human rights in some areas. Similarly, with our children, having systematic exceptions to the ethos of taking them seriously instead of coercing them, makes the whole idea incoherent.