"I may be wrong but I doubt this is possible in this game, or in real life."
It is, I basically want the be the Switzerland of the galaxy, but it seems you're right and that this game won't allow for that. I'll just build up a deterrent military and waste time researching stuff irrelevant to my preferred style of play. You'd think my complete lack of military in favor of diplomacy and trade would make me more of an asset to others in the galaxy but it apparently just makes me weak and something that needs to be conquered asap.
If this game's diplomacy model were applied to the real world the US would be invading Canada as we speak because it's weak militarily by comparison, and in general... Only they're our largest trade partner and viewed as an asset in real life. Whoever designed the diplomacy model and its criteria needs to take a Polsci or Econ 101 course at their local JC. This is basic stuff.
Actually, the United States DID invade Canada back in revolutionary times.
What the game isn't taking into account is geopolitical and geographical factors. For example, Switzerland is VERY protected by mountains making any invasion of them difficult. Nowdays there are many geopolitical factors as to why Switzerland isn't a huge target due to global and regional trade, international alliances, and resources. During WW2 Germany, for example, considered invading the Swiss but decided against it because it just wouldn't have been worth their time.
In a game like Gal Civ you generally don't have those problems, there isn't a reason not to invade. Basically, the game just isn't as complex as real life. These strategy games also have an inherent focus on military conflict which encourages the computer to act more aggressively. That being said, they SHOULD check to see if your a major trading partner or if you have any powerful allies.
Lastly, if you want to play peacefully and succeed you really do need to have an army. Few political and defense theories will support the idea of not having an army, it's just silly and is inviting trouble. I mean, if you want to reduce crime you wouldn't disband your police force would you? If you want more educated children your not going to disband your school district?
Build an army.
"If you want peace, prepare for war"