I don't see why mixing Tradition & Liberty is idiotic. If you have a very wide Empire, I think theres merit in filling out Liberty, then grabbing the Tradition opener & Oligarchy. Slow border growth & the lack of gold from the liberty tree makes those 2 Tradition policies quite attractive. If AIs covet your land & ate threatened by your city building, then you need a large army & the unit maintenance costs really bite into your budget. This also alleviates much of your need to keep buying tiles, again saving you gold.
Also Oligarchy is useful for defending cities.
I'm not saying you should always mix these trees but there can be circumstances where it can be valuable.
Also Oligarchy is useful for defending cities.
I'm not saying you should always mix these trees but there can be circumstances where it can be valuable.