Actually I don't believe that everyone roleplays. And people have different definitions of what roleplaying is and roleplay to different extents. And people don't always announce how they're going to roleplay, which further complicates things.
As for myself, I may decide roleplay about trivial amusing things that add flavor to the game or in special situations like a pre-made scenario, but I don't think it's entirely fair to use your roleplaying pretender god identity as someone to blame for your strategic decisions as a person, specifically in the case of the breaking of NAPs or other underhanded tactics. There's a person behind that fictional pretender god and that person should be responsible for what happens in the game.
Another problem is the fact that everyone seems to have a slightly different definition of roleplaying and we seem to go into it in an improvised and haphazard manner. While this can be fun, I think in a strategy game like Dom 3 it creates endless possibilities for for misunderstandings and miscommunication if not all parties on the same pages. Maybe it's just best to declare your role-playing intentions at the start of the game at least.
>"Your character is evil then play evil. If your character is good then play good."
You know it's rather complicated figuring out which nations are evil because everyone has a different definition. You may want to refer to
this thread for a discussion of which nations are evil. There's also a similar thread on who is good and how it is defined
here.
And just because a nation appears to be "good", does this mean they will automatically honor NAPs? For example, let's say Arcos signs a NAP with Nation X. Most people regard Arcos as a fairly honorable and "good" nation. But you could also come up with roleplaying reasons that explain there is an ambitious general working for Arcos who went ahead and broke the truce against everyone's wishes, and well crap, I guess we're in a war now. The point is you can make up flimsy roleplaying reasons to excuse anything, but you as the player, making the moves, are ultimately responsible for everything that happens in your nation and you should accept that responsibility.
Is Arcos evil? Most people regard them as "good", but they keep slaves to support their lavish way of life. How about Marignon? They are often regarded as "holy", but some people think they're like Nazis. I now believe that there aren't many if any "good" nations in Dominions. There can be a case made that all the nations are evil to some extent. If this is the case, the simple arithmetic of X is an evil nation and therefore it breaks it's NAPs, while Y is a good nation that honors it's NAPs falls apart.
>"Even if you send your NAPs to a neutral party, there is no guarantee that your ally won't claim that YOU are the one who violated it first! That would also be on the honor system, which is basically what this whole thing is based on."
You could send your turn files to that neutral party as well. Then there's a proof of who attacked who first.
>"I think carrying grudges across games is completely ridiculous and stupid, and anyone who does it is a worthless player."
However, I do agree with you here.
And the end of the day though, I believe that diplomatic functions like negotiating NAPs should be done out of character. This way the other player knows they are dealing with another person and not a fictional pretender god. I think this is a good thing, because then it is a basis for trust. Trust that is earned is valuable, and therefore you may not want to throw away it away in the next game by breaking a NAP.
You should assume responsibility for honoring or breaking the said NAP as a person, not as a fictional pretender identity that you get to throw away at the end of the game. As a result, you can let your reputation as trustworthy player hang on this instead of hiding behind fictional identities. This in turn forms a good basis for a community of players who may be more enjoyable to play with than roleplayers who will break a NAP a the drop of a hat and claim they did it because their pretender god made them do it. If every time I play a game with you, I am dealing with a brand new Pretender God X who has no history and suffers no consequences at the end of the game, then how can I trust you aside from measuring you against very relative standards of whether you are living up to the "goodness" or "evilness" of your nation, which is pretty much self-defined. As a result, you create a kind of fun-house world, where no one is really responsible. There's a time and a place where roleplay is fun, but I feel that too often it gets abused or trotted out as flimsy excuse for player decisions that were made for strategic reasons.