I always like to play friends with everyone but I watch a few playthroughs on YT and I see that most people just see stealing airships as a normal and needed tactic since building them consumes a lot of resources AND time (By late game I have maybe 3 ships and squads, 2 of them being manticores because it takes so much time to build in the beginning that I have to start the second ASAP). Comparatively, it's VERY unbalanced and leads to stealing as a necessity or at least a much better option instead of a roleplay option.
I feel like the mechanic in itself is fine, but remembering from my head stealing an airship gives a 20% decrease in relations. That's too little. If I was the leader of a faction and another faction attacked my installations and killed my soldiers, I would be damn pissed and that could outright lead to war.
My suggestion is this... a 40%-50% loss in relation to any type of attack should be a minimum. It would lead you to think twice about attacking if you do not intend to go to war with them, because today with a few pandoram colony attacks you can undo the damage and that's not fair nor realistic.
Worse attacks could lead to a bit more loss in reputation, repeated attacks should elevate the loss, and the current reputation could affect the relation - the more allied you are when you attack, a few more points are lost because you're actually betraying them.
If then getting airships become too difficult, the airship prices and build times could be toned down a little to compensate. That would lead players to actually choose between the 2 options instead of just stealing because its easily manageable.
Thanks for considering.