Movies rated R for one scene alone?

It is hypocrisy and the guidelines need to be re-written and perhaps another rating brought to light for US audiences. They can keep the current ones, but when there is a film with stronger adult content, but not of hard 'R' origins,  it perhaps then needs an un-restricted Mature rating, not an 'R' rating. As it stands, it gets discussed as though there are different levels of 'R' rating, soft and hard. This doesn't work within the objective reasoning behind the rating. Why should an amusing and harmless film be rated 'R' just for a sprinkling of four letter profanities, which then shares the same rating as a graphically violent horror film like Saw or Hostel?

The US also appears to have an issue with the NC17 rating, which most other responsible and level-headed countries don't have any issue restricting a film to over certain ages only pronto, in terms of its context.