In my current game on an immense map I ammassed over 40+ colonies, and figured what better way to build a defensive fleet than to use the ideaology perk of getting 3 defensive ships per planet.
I think this may need to be adjusted as it provided me with a huge fleet instantly. It should scale down based on the size of map you're in.
I'm hoping there's a planned overhaul for the whole ideology system. Currently doesn't work very well.