Military Tradition provides a free unit for the first army figure built during a turn. Military Tradition can be incredibly useful for staving off attackers and ensures that economy/culture/turtling techies will have a good catchup mechanic against more aggressive nations.
On the other hand, Pacifist only provides +2 culture max at the start of turn. Even for a culture player, isn't it still much better just to have the ability to build a decent military quickly?
Sometimes Pacifism is better. It can give you a GP faster by moving on the CT for free at the start of the game. If the GP is a General, then it can be better than having 3 free units that you can build anyway with your Cities.