1) Hydro wants to make sure Combat I (and any of the currently existing promotions) are not being handed out to units for free based on Traits so that it doesn't overlap with buildings and cultural unit special bonuses and so on. I suppose I can live with that but I've now proposed another design for the Aggressive promo.
If we are going to have Aggressive not giving out Combat I, then I think that a full +20% Combat is a little too strong but +10% is way too weak. I feel that Aggressives should have stronger attacking armies but since I'm listening to some of the above comments, I'm thinking that perhaps it should still be a notch better at defense than the norm as a result of basic overall improved warfare strategy from their leader. Thus, I'm proposing the Aggressive promo be:
This is possible with the new tags I added for generic only Attack bonus and only Defense bonus. It'd be nice to see them used here as their initial application.
2) Let me preface the following with the explanation that I'm stating this for the sake of discussion. I'm NOT dead set on either ALL positive nor ALL negative but find in this polar disagreement some fascinating underlying game design values being expressed that apply to a lot more than just this issue. So please take all of this as its intended, in a friendly discussionable tone

I'm probing for a deeper understanding of opinions here.
Ok, so I can understand the value in making it easier for players to more easily grasp the Positive/Negative traits. But do you really think its that hard to comprehend if there's some slight negatives on positives and vice versa? Its not like we have stupid players... some of the most intelligent gamers in the world would be drawn to this game no? Is simplicity really that valued a goal here? Particularly when simplicity is employed in such a manner as to eliminate meaningful depth of design?
Its one thing to have say, an Aggressive/Charismatic Leader with any old random negative trait attached, but its far more meaningful if the penalties they receive are the direct result of the positives they are getting, isn't it? Do you feel this meaningful linkage of penalty to benefit less desirable than making things more simple to grasp at first glance?
Is it better to have a game with a 'game' feel or one with a gritty feeling of 'model of reality' feel? I think that might be where the true value difference lies in this issue. And the funny thing for me is that in some cases I do feel that its possible to overly infuse realism to the point of making the game less enjoyable... I just don't feel this is really one of those areas.
3) You say they'd be easier to balance, but what if the bonus you wish to give is stronger than the norm? Doesn't it then make it easier to balance with a bit more negative to compensate for that? If we rule out having negatives on positive traits, I was finding in reviewing and proposing my suggestions that there was far less maneuverability in which to operate. Otherwise, if you give one trait a decent enough benefit that it breaks the balance between the positive traits, then we need to go through all other positive traits and add to them rather than pulling the trait back into balance by penalizing it a bit more. There were a few specific cases where the trait struck me as being capable of a lot more than most but also would've had more drawbacks than most so it made sense that way. Again, this is not to 'argue' but to give some thoughts for consideration and to drum up some equally pointed replies.