At its most basic, roleplaying answers the question, 'What will my character do now?' Referring to one's character in the third person all the time is no less roleplaying than speaking only in-character. The is no purity or superiority in the latter approach; I personally enjoy first-person, in-character dialog, both as a player and as a referee, but I don't think less of gamers who prefer the remove of, 'My guy says . . .'
With that in mind, we can dispense with the notion that social skills diminish roleplaying any more than any other skills do. The overwhelming majority of the roleplaying games out there include some sort of rules for social interaction, whether they are as basic as reaction and loyalty rolls in D&D or as involved as Burning Wheel's Duel of Wits. The notion of resolving social interaction through 'pure roleplay,' without some sort of recourse to the rules, is limited to a tiny handful of games, or to gamers who choose to ignore the rules in games which include them; in my experience, the latter are far more common than the former.
So why do some gamers have a nutty over social skills? In my experience, there are a couple of reasons for this. First, some gamers are of the opinion, 'I can't thrust a rapier or swing from a chandelier at the table, so I need rules and rolls for those, but I can just say what my character says, and I don't need rules for that!' That's certainly true: adjudication of non-player character reactions can be handled by the referee without recourse to a die roll or an attribute score, but once again, very few games actually leave social interaction solely to the referee's discretion. The norm is to include rules for resolution, whether those rules are rendered with a broad-brush or crafted in intricate detail.
Second, some games give social skills a bad name, though not always deservedly so. Tales of d20 'diplomancers' optimised to take advantage of the Diplomacy or Bluff or Intimidate skills, breaking entire campaigns by turning a social skill into a form of mind control, can be found in the many different corners where gamers gather, on- and off-line. Despite the fact that at least some of these stories come from misinterpreting the actual rules associated with the skills, they reinforce the predilections of those who prefer to remove or ignore most or all of the rules for social interactions, or more rarely to find those few games with no such rules at all.
Third, as noted right at the beginning, gamers conflating roleplaying with in-character dialog - the 'amateur thespians' - express the opinion that social skills 'inhibit roleplaying!' by 'reducing social interaction to the roll of a die.' I think that's bollocks. Consider the following.
Example 1: "Ahead of you, on a curve in the stream, is a stone bridge. A carriage is overturned at the far end of the bridge, creating a barricade blocking passage to the road beyond. Behind the carriage you see the tips of a dozen pikes above an equal number of gleaming morions. To the right, across the stream, just inside the tree line, is a hastily-built stone revetment, and behind it the light through the trees glints off the barrels of a half-dozen arquebuses. Because of the curve in the stream, the revetment is at right angles to the bridge, giving the arquebusiers a clear field of fire across the open ground approaching the span."Here's the thing: social skills are used to resolve your attempts to accomplish a task. They don't do your roleplaying for you.
"Uh . . . I roll for Tactics."
Example 2: "The king's minister, Enfou, pulls you aside as dancers swirl to the musicians huddled in one corner of the ballroom. 'The king is desperate,' he says. 'The baron de Bauchery can raise enough mercenaries to defend the frontier, but he refuses to do so unless he the king promises him Princess Pinkflower's hand in marriage. Meanwhile the conte di Grognardo is the best commander we have, but he refuses to serve under de Bauchery, and he wants the princess' hand for his son.'"
"Uh . . . I roll for Diplomacy."
In the first example, you, the player, need to decide how the adventurers are going to get past the soldiers holding the bridge, and in the second you need to figure out how you're going to resolve the conflict between the courtiers in time to get the soldiers to the front. Your character's social skills resolve how well you accomplish what you set out to do.
Moreover, social skills are not charm spells. A non-player character made Helpful through the Diplomacy skill in d20 may be willing to take considerable risks on behalf of your highly persuasive character, but that doesn't make the npc a thrall. The npc will still look after his interests and pursue his agenda while offering assistance to the adventurers.
I've used rolls for social interactions in every game I've ever played, from the aforementioned Charisma-adjusted reaction rolls and loyalty scores for henchmen and hirelings in AD&D to the Contact rules in Top Secret to the social skills of d20 and now Flashing Blades, and in my experience they neither inhibit in-character dialog nor do they result in the players substituting skill rolls for actually having to figure out how to best use those skills to get what they want.
Now, if a game's social skills are being called into play, it follows that the stats of both player and non-player characters come into play. Next up, a quick look at stats for non-player characters.