Is keeping my monastery a good idea

So i just defeated that angry cuck Celeas and i got the treasure that i wasted tons of negotiations and a lot of manpower on, The monastery.

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I know its a one of a kind and people say your better off deleting it if you want more defence, but i feel like keeping it anyway because it

A. looks nice
B. good enough bonus
C. There is one of it, you can build 5 billion churches but can have one monastery