I agree with this: a pre-emptive strike is just as bad as the defender as the attacker.
I think this is yet another reason to get rid of altogether ridiculous and pointless "declaration of war" rules. All they do is cause arguments, and limit the very interesting aspects of *diplomacy* that people are apparently playing for.
If you want a mostly peaceful game, use settings to achieve that. For instance, a very high defensive kill percentage will achieve your desired outcome quite nicely. :)
I've spoken of this before here:
https://www.warlight.net/Forum/160624-diplomacy-dumbies