These are good questions."Who are rules written for in games?" or "Should games include rules that could help shape the play of beginning players and give help to reign in the really bad ones... even if the long term better players will never need them?" or "Do we really need the rules to punish cheaters and encourage good RPing?"
Why do other types of games and sports have rules for punishing cheating if the good players we want to play with wouldn't do it? Did Gygax need to include the things about dealing with disruptive players if we've never needed them? Do RPGs really need a point buy system for ability scores (last 1e game and all the VtM games I've ever played the GM's trusted us to pick our scores and we didn't abuse them)? Should an RPG be designed around roles and niche protection if an experienced group of players already knows that?
I see rules for games, in general, as having several functions. I'm not sure I can itemise them all. But at least two I can think of are this:
* to create parameters for choice that will be mentally, and perhaps emotionally, stimulating/engaging;
* to manage conflicts of interest between and within participants.
* to manage conflicts of interest between and within participants.
The first of these is obviously highly subject to taste. Just focusing on RPGs, engagement in a typical game of Tunnels & Trolls (wacky spell names, ultra-random PC generation, rolling buckets of dice in combat) is generated quite differently from BW, even though the latter can also involve handfuls of dice.
The second is, I think, more amenable to analysis and design, at least in terms of identifying conflicts, although decisions about the best way to manage them will again be highly taste-dependent.
The most obvious conflict of interest in an RPG is that the typical player wants his/her PC to succeed in challenges, but the game is more interesting when the outcome is (i) unknown, and (ii) contains the potential of adversity. Hence the need for a GM. (Although what exactly a GM should be doing is different for different tastes/styles - contrast, say, Gygaxian "skilled play" with indie-style "scene framing" play.)
Points-buy for PCs is another example of managing conflicts of interest, though different games take different views on what is worth points (eg Burning Wheel makes disadvantages cost points, the underlying logic - as I see it - being that the increase these give to spotlight time for that PC's player is more salient than the burden it imposes on mechanical effectiveness).
Is playing a character who is not amoral or psychopathic - who follows some sort of code or adheres to moral requirements - a source of conflicts of interest? In Gygaxian play, I think the answer is "yes, it is", because skilled play depends in part upon a willingness to use any suitable tactic for victory (so-called "combat as war"), and having a code or moral commitments puts limits on this. Hence, in this sort of play I think it makes sense to have the GM police the players of such PCs to make sure that they stick to their codes. Arguably, such players also get a compensation in the form of a PC that is mechanically better (many see the paladin that way, though I personally have my doubts given the need to put a 17 in CHA and the higher XP costs). And whether or not you are a paladin, being Lawful and/or Good does give you other mechanical benefits, like access to healing magic from NPCs, better loyalty from hirelings and the like.
But I think in many, perhaps most, non-Gygaxian games there is no conflict of interest in playing a non-amoral, non-psychopathic character. (Indeed, in a lot of 2nd ed style play playing an amoral or psychopathic character is a good way to get hammered by the GM, not just through alignment rules but via 10th level town guards who lock you up in gaol etc.) Exactly how this relates to the "Hickman revolution" is probably a complex question, and I think there are non-Hickmanesque pathways (eg my own), but it is clearly connected to the idea that RPG play is in some important way linked to story and not just to self-aggrandisement. (Runequest is a pre-Hickman manifestation of this idea. Classic Traveller is interesting - should we see a world's Law Level as an alternative to alignment mechanics? But as one that can also underpin a change in the orientation of play from sheer self-aggrandisement to something involving world and story?)
At this point, it's not clear to me that alignment rules are needed to avoid cheating. (Though the history of the game shows they have come to be adapted for other purposes, most obviously being to serve a function for the GM in world-building and for the players in defining a personality to play to.)
Some of Gygax's broader advice about disruptive players I regard as completely misguided. Professional football needs rules for what happens (for instance) when one player punches another in the jaw, because it is a high (financial) stakes game where the standing temptation to lay out your opponents by way of physical violence is obvious. But when I was a kid playing football with my friends during school lunchtime, we didn't need a rule for that. Because no one was going to punch someone else out, and if they did the solution wasn't part of the game, but rather lay outside the game (eg calling a teacher, or perhaps punching them back).
Similarly, if you buy a Monopoly set or a chess set, it won't include in its rules what to do if someone steals money from the bank, or tips over the board in a fit of pique when they realise they are in a losing position. The rules take for granted that the participants are committed to the basic endeavour of playing rather than spoiling the game. Unlike in professional sports, the rules assume that playing the game is an end in itself, not just a means to some other (typically financial) end which then creates standing temptations to cheat.
I see RPGing the same way. The rules should be written on the assumption that the players of the game want to play the game as an end in itself. And the question with what to do with cheaters, or punchers, or board-tipper-overers is not itself part of the game rules. It's a social question that can be handled via social means.
If the game designers think there are bits of the game that are particularly likely to lead even normal reasonable people to want to cheat, or punch, or tip over the board, then that is a further matter. Perhaps those parts of the game should be flagged as problematic, and alternatives given. Maybe they should be eliminated? That's not obviously the case - for instance, part of what makes the temptation to punch in Australian Rules football particularly strong is that the game permits a high degree of reasonably violent conflict, and so - unlike soccer, say - generates circumstances where physical violence is already taking place, and a punch may not be that much of an escalation. But that's not necessarily an argument to reduce the physically aggressive nature of the game, which is a good part of its attraction as a spectator sport.
Perhaps it is inherent in Gygaxian play that players will want to cheat rather than be thwarted and frustrated by the GM's clever tricks and puzzles. So perhaps part of what makes the game interesting is also what makes it prone to generate cheating. (Like looking at the back of a riddle book to get the answers to the riddles.) Maybe this is what Gygax had in mind in at least some of his advice on how to handle disruptive players. (Though I still think "ethereal mummies" are just a hopeless technique - has any one (Gygax or other) ever used them in a way that worked?)
But as RPGing becomes (on the whole) less Gygaxian, do we still need such advice? At least it might be better if it was more closely connected to those features of play that make it necessary.
There is a whole other dimension of "disruptive play" which I don't necessarily think Gygax had in mind, but came to the fore in the 2nd-ed era, which is associated with players who want to jump the GM's rails or "disrupt the plot". But I don't think mechanical alignment is a very suitable way for controlling those players. (Though my sympathy for this whole playstyle is not really strong enough to make me suited for analysing its techniques with any sophistication.)