Apologies if this has already been covered ... there are so many threads ... but I'm seeing these problems with DOAM:
1) It scales terribly. How far you were from hitting makes no difference to the result.
Now, damage on a near-miss seems to be more sensible. But, D&D has, except in a few rare cases of optional or home rules, not gone down the route of detailing nears misses, or complete misses, or just barely hits, or strong hits. There *are* fumbles and crits in 3E, and those are set to the maximal results, so that sets a precedent to start considering the attack result vs. the target number as a measure of the result. But, we just haven't gone there, and the game seems to have long decided to not go there.
2) It requires wholly new mental gymnastics to explain. That is, we already have to bend (and bend, and bend) to explain hit points and attack rolls, and really only go so far before giving up and accepting the game mechanics as is, since they make for a decent game anyways. Why invent this new mechanic?
3) 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?
4) It creates a new narrative niche which begs for an explanation. Does the damage represent effort expended to avoid an actual hit?
5) 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. Now, mathematicians often do this when exploring mathematical models of physics, and can arrive with new implied physical processes as a result. But, they can also arrive a non-physical situations. In the underlying game world, perhaps there is something there to be discovered which would explain damage on a miss. But, asking players to make that discovery is asking too much. The rules author really has to present a case to justify the abstraction -- that's their job, not the players.
Then, if there are these objections, and they seem to be real objections, the onus turns to the rules author to demonstrate that the new rule is a good idea. That, the new rule adds a value which is greater than the objections.
Thx!
TomB