For Iserith and those arguing with him, let it go; you're not going to convince anyone or change anyone's mind at this point, and there are really no further new points to be made on that particular front. Everyone knows where the lines are drawn, and as long each one works for the respective games, that's all that really matters. Both interpretations are as right and/or as wrong as the individual group is willing to accept, no more and no less.
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For Shirebork: Because intimidate, deceit, and persuasion are no different from any other skill, class ability, or magic ability available to both NPCs and PCs in the game. For all that I can respect and understand Iserith's position, and seen a few others that hold it, it's not particularly common, and very few groups are going to make it a major concern. Very few people I've met in the many circles I've gamed in, be they DM or player, treat those three skills (whatever their name is in any given edition) any differently from the limits put on a character from failing a spot/perception roll to see a stealthy NPC, imposing a condition like poison or nauseated, or using magic. All have had more or less the same effect in pretty much every game I've played in, and if anything, magic is tamped down and limited on the NPC side far more than anything else, not the social skills. And that is generally how I run games; I don't usually bring any one tactic, skill, magic spell, etc. to the forefront unless it's something that is relevant to what the party is doing at that particular moment. At the same time, I see no point in removing a perfectly good tool from list of options to throw at PCs when it works just fine for what it is designed to do and very few people I have met treat it as a major concern, either in my games or any others I've been in. Most have been perfectly willing to accept that their characters can and will have hurdles put in front of them making certain paths harder than others in any given circumstance as long as the path is not shut down entirely and/or the player is not forced to go down a truly unpleasant path; many have seen such things a proper challenge to be relished and others have used the mechanical aspect to start from with the positive end result that neither DM nor player would have expected that would probably not have happened at all if the initial response had been left up entirely to player.
In most games I've been in, to have any of those three skills come up at all is a relatively rare event anyway, and when they do, it's usually a quick dice roll and back to combat, so the idea of using it on PCs hasn't really offended anyone when the impact is minimal regardless. In a more investigative type encounter, campaign, regular use of these skills is far more prominent and appropriate going both ways; PCs potentially being deceived, intimidated or persuaded to do things not automatically in their character concept would not only be normal, but a key element of such campaigns or encounters. I actually have several potential plots brewing in my world that will come out with the right group and right time that will absolutely involve heavy use of these mechanics going both ways; I say right group and right time precisely because I fully understand that not every group is going to be up for that particular type of campaign. Still, I will often pull them out for a scene here and a scene there in other campaigns as a break, transition, or simply a way for the PCs to gather information about the world.
The key to me is that most players don't actually mind it being used against their characters as long as it's appropriate to the story and reasonably balanced in it's use (relative to both how other skills are used and how effective PCs are allowed to be with them on NPCs), and I have never seen in any games I've been in any complaints about a player being told "you're intimidated" or something similar non-flowery unless it was tied to specific circumstances of a larger issue. In most games I've been in there has always been a large amount of "if the PCs can use it, so can the NPCs potentially," so people are generally well aware of what they might be facing on that front well before it comes up. So while I can understand where Isireth is coming from, I cannot and will not pretend to understand the inflexibility of his position. While a perfectly legitimate place to draw that firm of a line, to me it feels like a really weird and awkward place to do so, and it's been an insightful discussion, even if it will have zero impact on my own personal game.