Quoting parrottmath, reply 14
What about the naval manufacturing ports in the US? They do not have much defense to withstand a military assault. Although, there are plenty of protection provided from the navy ships in the area, but nothing at the actual port itself. Why would this paradigm change when it come to space?
#1 reality takes a back seat to game balance.
#2 the troops defending the naval shipyard in your example can be considered to be the innate defenses of that naval shipyard as we never leave our naval shipyards undefended and especially not during wartime so your example in itself is flawed.
#1 Yes, reality does take a backseat to game balance, but it does play a role. If I draw a BIG sword on a game, I would expect that sword to do more damage than a little sword. But, it has nothing to do with game-balance. I could set it up to say you get the Gobsmack as the initial sword, and toward the endgame, you get the house hold butter knife. But for game balance we need the house hold butter knife to do more damage than the initial Gobsmack sword by a factor of 10. Reality does play a role in a game. You need to be reasonable with the choices. The above has already been stated as fictional, but I'm also stating that for defense mobile defense is always better than stationary defense. I don't recall people complain in starcraft that my factory I built cannot defend itself. I need to put troops nearby to defend it. How should this be any different in GalCiv?
#2 For naval shipyards that is true, but the US doesn't build all their ships at the naval shipyards. There are private shipyards that build quite a few of our naval ships. There are corporations that build assualt vehicles that do not have their factories defended against a military assault. I'm not talking about a the security necessary for local protection, I'm talking on a military (large) assault on a private shipbuilder. Most of the naval shipyards are defended by the ships in port and are payed for daily. Even automated defenses need to be maintained and payed for constantly.
Fine non-reality based reason...
For Gal Civ, the balance would require a maintenance cost on the shipyard for the military module to be added. If we do go this way, it still would not sate the problem of Drengin have fighting units before me, because your shipyard would still be vunerable. The Drengin would just have to build 2 ships to destroy your initial shipyard or just surround it like a planet until they can destroy it. It is a gamebalance that has NOTHING to do with a shipyard. Remove the shipyard, leave only planet building of ships, then Drengin could just surround your initial planet, you being unable to defend against it would have to wait to research something to defend yourself from this. But you still wouldn't be able to produce strong enough ships to stop the Drengin blockade which has been building them since the beginning of the game and slowly growing since they are not restricted as you are from colonizing new worlds.
Also, if the enemy is capable of destroying your shipyard, then they should win... check-mate style. If I rush you in starcraft and destroy your initial barracks it is check-mate just the same. In chess, you can lose within 4 moves.
The AI should realize that it needs to defend it's shipyards. The shipyards do effectively eliminate the "I need to invade every planet you own." You are able to station units in the shipyard for the defense of the shipyard (a.k.a. you have just added a defense module to the shipyard). So, for the original post it already has the capability to defend itself by you stationing fleets of ships there.