I'm sorry, but these cultural/political/territory borders (whatever you want to call them) are implemented CORRECTLY in GALVCIV2.
I believe we have all just become accustomed to Civilization-style border behaviour.
Here on earth, there is NOTHING stopping Canada from moving our troops into the U.S. and setting up a military base etc.. EXCEPT the fact that the US "might attack", "might use diplomacy, the UN etc.."
The US has declared cocaine illegal within their borders, but that doesn't stop drug smugglers from bringing it into the country!! It's up to the US to patrol their borders to detect and prevent it.
And the earth is just a couple million square miles........ space is ............ well...........INFINITE........
Civilization just automates the process of declaring WAR as soon as someone enters your territory (without Open Borders)....it still doesn't prevent you.
But there does need to be MORE diplomatic activities (e.g. war declaration, open borders etc..) around cultural/political/territory border incursions IF DETECTED.
-- just my two cents