The way I see it (from a technical point of view)- deleting a turret takes just 15 seconds- 5 seconds to delete it in PCS, 5 seconds to click on Notepad, and 5 seconds to disable the turret's .tbl entry.
If someone wants an unarmed base, it's just a few clicks away from it; if someone wants more turrets- the existing ones can be copied and moved around; but importing a turret might be a bit more of a hassle (import turret model, textures, rescale to fit the ship model, etc).
As such I suggest putting a couple to fill out empty space, to make it easier for other modders if they need to play around with the numbers and placements of turrets.
In fact if I ever make a 2nd iteration of T-M ships, the turret barbettes will all be separate subobjects from the main hull for easier (re)moving.
From an in game perspective- I'm quite sure the Elysium is used for civilian purposes and it does have a turret; guess that's the FreeSpace way of doing business- somewhere in the timeline a lawyer decided that the 2nd Amendment applies to space ships.