I think the biggest problem here is the use of the term "ZOC" as in zone of control, when in GalCiv you don't have a "zone of control". Nobody controls space in GalCiv. Space is like international waters.
So when the term "ZOC" is used, of course people will not understand why other players can fly and build freely in their ZOC. Because naturally, when you control an area you expect that others need permission (for example in form of treaties) to enter your space.
But there is no ZOC in GalCiv, there is only a zone of influence (ZOI) - a zone where your culture is the dominant one. From this perspective it is logical why in GalCiv space is open for anyone unless there are treaties made to restrict this freedom - and not the other way around like mentioned above. It also makes it understandable that any starbase will create a such an ZOI, if there is no stronger ZOI in place.
So please, stop thinking there are ZOC in GalCiv and start thinking in terms of ZOI. It may be different from other games, but since it was fun in GalCiv 2, I'm sure it will be fun in GalCiv3 if you accept the concept.