It requires wholly new mental gymnastics to explain.
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It creates a new narrative niche which begs for an explanation.
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It breaks the abstraction model by adding a new mechanic which is defined in terms of the abstraction, not in terms of an underlying imagined world.
As far as I can tell these are all the same complaint.
Combat in D&Dnext (as in 3E and 4e) is broken up into 6-second chunks. Those chunks don't, in themselves, correspond to any event or process in the gameworld. Some physical processes in the gameworld - say, the swing of certain pendulums - have periods of 6 seconds, but combat is not one of those processes. The 6 second round is simply a metagame device for regulating the action economy.
As part of that action economy, the combat output of the typical character is determined by making 1 attack roll per 6 second round. That roll does not, in itself, correspond to any event or process in the gameworld. The combatants in the gameworld are (presumably) fighting much as real people do in the real world (or, perhaps, like fantasy people do in fantasy movies). They are not tocking at one another in a stop-motion fashion.
For the typical character, a successful to hit roll (" a hit") means that, in that 6 seconds of combat, the foe was worn down. In the fiction that could correspond to one mighty blow, multiple lesser blows, a flurry of skilled swordplay that left the foe somewhat exhausted, off-balance etc. The extent to which you want to treat this as some form of meat-ablation is up to you, although by default in D&Dnext, it's not meat until the foe has lost half their hp.
For the typical character, a failed to hit roll ("a miss") means that, in that 6 seconds of combat, the foe was not worn down. In the fiction that could correspond to blows successfully parried, or deflected off armour or a shield, or dodged, etc. Admittedly my grasp of the details of melee combat is limited, but it seems to me only in certain corner cases (eg a normal person dodges a giant's club or a dragon's bite) is the game mechanical "miss" likely to correspond in a literal sense to a series of swings which never connect in any physical way with a foe or his/her equipment. (Extra oddities arise in that, in the mechanics, it is possible to dodge a giant's club without yielding any ground, whereas at least in all the movie depictions of that sort of dodging I'm familiar with the dodging involves running about, to take advantage of the small target's manoeuvrability advantage over the giant, dragon etc.)
So far, none of the above considerations have factored in DoaM. They are just extrapolating from the mechanical logic of D&D combat plus my own common-sense (?) understanding of the physical realities of melee combat.
What difference does DoaM make? It means that, in 6 seconds of melee combat, the GWF cannot but wear down his/her foe to some extent. The function of the to-hit roll, for that character, is not to decide "whether or not", but rather to decided "how much?" (The two alternatives being STR or W+STR.) This does not "break the abstraction". The only "explanation" or "mental gymnastics" required is to imagine a fighter so implacable that, in 6 seconds of combat, s/he cannot but wear down his/her foe to some extent. That doesn't strike me as very hard.
Now for those who are
not treating the action economy, the 6 second round and the attack roll as abstractions, but are treating them literally - as in, each combatant literally moves his/her weapon once per 6 seconds, and a weapon makes debilitating physical contact with an opponent at most once per 6 seconds (corresponding to a literal "hit"), and a "miss" on an attack roll is literally that, ie a blow which failed to make any sort of physical contact with an opponent but rather found only empty air - I can see how DoaM might be a problem.
But that is not because it breaks the abstraction. That is because it relies upon treating the combat mechanics as abstractions, rather than literal representations of physical movements by the characters within the gameworld.
(I regard all of the above as just spelling out, in a bit more detail, [MENTION=87792]Neonchameleon[/MENTION]'s analysis in the OP.)
It interacts with other rules in strange ways. For example, often, an attack must deal damage for a poison effect to occur. Would poison apply on a miss?
I took this to be what Mearls had in mind when he said on Twitter that DoaM causes some head-scratching at the table. If you are going to use it, you need to differentiate, in your statements of mechanics, between events/effects that trigger on a "hit" (ie a successful attack roll) and events/effects that trigger on the infliction of damage (which, for a GWF with DoaM, is any validly declared attack). This requires suitable drafting of rules text combined with a good sense of the desirable probability distribution for various effects.
To take your poison example: if it is a necessary condition of inflicting a poison effect that damage be dealt (that is not the case in 4e, nor I believe in B/X or AD&D, but might be in 3E for all I know), I think it would be a mistake to make that a
sufficient condition. For balance reasons, a DoaM fighter who has poisoned his/her weapon should still have to roll a successful attack roll to deliver the poison.
No one who likes DoaM would have missed it if another equally evocative but inoffensive option had been offered.
Obviously by "no one" you don't literally mean "no one" - so the fact that I'm a counterexample to what you say isn't refutation on its own. But what is the evidence that I am a solitary, unrepresentative prospective customer?