Starfox
Hero
Building upon the perspective that Mike Mearls offered in his last Ruling Skill Challenges column, I would classify social skills as follows. Bluff manipulates an NPC's perceptions and expectations, ideally preying on his character weaknesses. Diplomacy appeals to an NPC's motivations and values. Intimidate preys upon an NPC's fears. What matters is not what the PC says but the effect they're trying to achieve.
I like this description of what the skills do and divinding it based upon what aspect of the target's personality you are playing on. In my homebrew, I have two interaction skills, Charm and Impress. Charm works by fattening the listener's ego, playing to his expectations so that he considers you reliable, and projecting a friendly image. It corresponds to Diplomacy and Bluff in DnD. Impress tries to make the listener submit to your superior abilities, and includes what Intimidate does in DnD but also has many leadership uses.
Imagine the SEALs nat oned on their intimidation check. They still have guns. Maybe guns give such a bonus to intimidation that it's essentially auto-success?
A modifier, yes. Auto-success no.
Imagine a bunch of seals busting the door of a high-profile lawyer. The lawyer is unlikely to physically resist, but he will know enough and have enough backbone to not really be intimidated either, perhaps actually making the SEALS uncertain of their right to be there and afraid of the consequences.
Or busting the door of a terrorist nest. Or bank office. Or the lobby where the loyal butler is guarding his mistress' privacy as she entertains her lover in the back room. Or a dissident newspaper office. Or, if they are SS and not SEALS, the French resistance? In these situations, a roll is definitely called for. And the troopers need to be trained to act in in an authoritative manner to impose their will without bloodshed. Whereas the Cha 4 fighter might have to resort to violence, because his shifty eyes, bad posture, and overall uncertainty makes people not take him seriously. He simply does not look confident enough to use his weapon. A person with Insight/Sense Motive might perceive him as a real threat and react based on this, but that is not successful Intimidation. In-world, his consistent failures to impress would have conditioned him to shut up, either becoming a silent killer who just skipped the intimidation phase or the henchman of some higher-charisma boss.
The problem is usually with assertive players with a reasonable RL Charisma used to getting their way in-game by acting out the intimidation, effectively intimidating the other players and GM. This is actually really bad roleplaying.