I'm afraid the war tax is imposed on any nation at war, whether you were the aggressor or dragged into it doesn't matter - which can be annoying if you're getting swarmed while trying to live up to the UP ideals.
You don't need to annoy the Drath for them to find someone to fight you. They don't even have to know you. They'll just start proxy wars because they can - oh, and they're the humble, good guys. It's a rough galaxy out there.
I doubt the situation is intentional - though only the developers can answer that question with certainty - but whatever the case, it's there now. The only sure way to avoid getting dragged in wars is by building up a decent military. In the end, that's what counts although other skills such as diplomacy will give you some more leeway.
When nations declare war, there is a period of time they won't be willing to speak. After a few turns, they will be open for negotiations again. Being a super-diplomat will shorten the period of diplomatic black-out.
