It is strange that the walls of the liberty policy are given to newly conquered cities. It makes conquering and keeping very easy.
Based on my experience, I'd say this is a
positive consequence, and would choose vigorously to keep this effect. If not in Liberty, maybe in Honor - but somewhere, please.
Capturing enemy cities seems by far the riskiest action one can take with a military unit. No matter how diligently one works to clear out all the enemy units in the area, the AI far too often manages to conjure up a half-dead carrack or arquebus or whatever, seemingly out of nowhere (a "rallied partisan" maybe?) which sweeps in next turn to retake the defenseless city.
This wouldn't be such a problem, except that the garrison (capturing unit) is killed in the process. A warmonger has no more valuable commodity than veteran troops, and losing a level 6, 7, 8 unit you've had since you discovered the wheel in this way is totally lame and depressing. I have no doubt I lose more troops this way than in proper combat.
It's so bad, I'm reluctant to take a city with a unit that can't move back out the same turn. That's right - the only surefire way to preserve my troops is to
abandon a newly claimed city, let the AI recapture, and repeat. It's quite ridiculous really, and entirely too easy for an overmatched opponent to exploit.
To that end I think a defense building or at least some health for newly captured cities is a preferable arrangement. Not back to their original health and defense, by any means, but enough that retaking needs a halfway legitimate counterattack, not just a lonely ninja boat.