In your OP your saying the consequences of your PC actions should also be determined by you and what you think. You can decide what you want to do all day long, but the DM gets to decide the consequences/results of your actions all day long. That is not dictating, that is how the game works, that is how real life works.
I'm not sure what you mean here by "consequences of your action".
If we put to one side the case of PCs like paladins and clerics, who are liable to falling, then the main consequence of a GM's adverse alignment judgment is that it is now official, at the game table, that my PC is (let's say)
evil, even though in my opinion as a player what my PC was doing is
good. In my real life, at least, there is no equivalence to this - when I evaluate my own conduct, whether aesthetically, or morally, or . . ., that is my evaluation and it stands until I revise it. I might revise it after conversation with others - whether my partner, my friends, or (in the case of a religous person) my priest or even the "conversation" of prayer.
Likewise in the sort of approach to play that I am advocating, the player can talk to the GM, his/her fellow players, or anyone s/he cares to about what her PC is doing. In light of that, s/he might decide eg that it is time for her paladin to atone.
But I continue to assert that it is a needless recipe for conflict to give the GM the power to unilaterally override a player's evaluative judgements at the game table. Some people, at least, think a good rule of thumb for avoiding awkardness at dinner parties is never to discuss religion or politics. Alignment rules turn this on its head, by mandating that the GM continually express his or her opinion of the evaluative judgements that the players express via their play of their PCs.
You said that you should get to decide not only your actions, but how those actions are reacted too.
By whom? I never said that the GM doesn't control NPCs. I did say that, in a game in which divine PCs depend upon the favour of the gods, then it is a mistake to treat the gods as NPCs purely under the GM's control. But I'm not saying that this is a mistake in the sense of a careless misclassification. I'm saying it's a design mistake - and it's a design mistake, in my sense, because it leads to needless conflict at the game table.
Consider a game in which a player is allowed to spend PC-building resources to buy a sidekick, a lover, an enemy, whatever. If the GM then proceeds to play that person as an ordinary NPC - fodder for casual assassination by other foes, prone to treachery, or (in the case of a PC-purchased enemy) able to be overcome with the same ease as a typical orc warrior - then in my view the GM is doing it wrong. Because if this happened, the GM would in effect be depriving the player of the benefits of the play experience that s/he spent resources to buy.
Well, a player who plays a cleric or a paladin whose powers are dependent upon divine favour has payed PC-building resources - choice of character class, in typical D&D - to get the benefit of a certain play experience, namely, playing a holy character in a close relationship to a deity. If the GM treats that deity like any other NPC, as his or hers to play independently of the preferences of the player who has spent resources to make that deity a salient element of the game, then (in my view) the GM is doing it wrong.
If you want that, be the DM, they get to do that. All you control is what your PC does, everything else is decided by the DM.
No other player of the game is at the whim of the GM in this way. The GM doesn't get to decide whether or not what the player of the fighter chose to have her PC do is tactically sound or not - the GM might have an opinion, but so does the player, and the player is not obliged to change her mind just because the GM disagrees with her. My contention is that players of divine PCs, in choosing what their character does and what it's evaluative significance is, shouldn't be subject to GM dictation either.
Alignments sole purpose is to give a common ground definition of what is expected of your PC when that alignment is put on their character sheet,
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Players who fail to do so simply fail to do so. So suffer whatever consequences the GM feels are appropriate.
I'm not sure how carefully you've chosen your words, and so I don't want to seem like I'm making a cheap point. But to me there seems to be a pretty big difference between "a common ground definition" and "consequences the GM feels are appropriate". Because the second phrase removes the common ground altogether - it is the GM's opinion that is relevant.
why even bother with having a DM? Why roll a D20 to see if you hit or saved?
I don't quite get the point you're making here. A GM has a lot of work to do - mostly, when I GM, I see myself as (i) providing the backstory, and (ii) providing the antagonists to the PCs. I also (iii) do a fair bit of the narration of what is happening during action resolution, because most of my players are a bit slack in this respect. And perhaps most importantly, (iv) I adjudicate action resolution when the mechanics of the game set the parameters of an outcome but don't fully dictate it (in 4e this mostly comes up in skill challenges, but also from time to time in combat).
I don't see it as my job to pass moral or aesthetic judgement on my friends
as an integral part of playing the game. (From time to time I do express such opinions, but they are simply the opinions of a participant in the shared game - they have no special force coming from my status as GM.)
If you're saying, on the other hand, that alignment rules are as clear as (for example) saving throw rules - so anyone who is capable of working out whether or not a given d20 roll has or has not resulted in a save is equally capable of working out whether or not some action is good or evil, in such a way that non-collusive agreement is obtainable by all participants in the game - then I simply disagree. And I'll simply repeat the example I gave upthread - look at the reactions in Pakistan to the recent political assassination in that country.
All of that's fine. But I see no reason why the DM needs to 'get involved' here.
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IMO just let the player role-play as they see fit, no need to 'check' there behavior against some kind of code or alignment.
If NPCs watching the fight have an opinion they can act on it; otherwise I see no need to 'second guess' how the player is role playing.
This really sums up my view pretty well.