I can think of a lot of lines I would defend that sort acts of influence into socially-acceptable and not, or moral and not, or pragmatic and not, or various other divisions. But I agree with you that none of those lines are between influence and manipulation (nor between manipulation and coercion, nor between coercion and force).

I wouldn't expect them to be: manipulation, coercion, and force are all sometimes socially acceptable, moral, and pragmatic.