There are many vents on JB, some of which make sense for them to be KOS, others not. My definition of a "vent" in this case is a breakable texture (wall, vent, etc.) which lead from one area to another without use of teleportation.
Examples of vents that are KOS and make sense:
ba_jail_minecraftparty_v6: vent from last cell to medic
This makes sense because the vent takes you to an area outside of your cell before cell doors are open, giving you an advantage over the CTs.
Space Jail: vent in cells which lead to armory
This makes sense because it's a secret which leads to armory, giving you an advantage.
But there are some vents which don't make sense as KOS areas:
ba_mlcastle_se: vent between cells
This doesn't make sense because it offers no advantages other than letting you hop between cells before cell doors are open. It doesn't lead to any KOS area, and it doesn't make a CT's job harder to keep track of Ts. However, because it's technically a secret, some CTs have been killing Ts for using this.
Spy VS. Spy: vent in cell which gives you a smoke and a spy mask Removed because this is a secret, not a vent
This doesn't make sense because it's not taking you outside of your cell nor is the area inside a KOS area. Furthermore, it does not hinder a CTs ability to keep track of Ts. Indeed, I have never seen any CT shoot/kill a T who has gotten the smoke from this "secret" through the vent.
Let's take a look at another KOS area, teleporters. Most teleporters are KOS except for ones which absolutely cannot be avoided, like the teleporter between first and second island on Clouds. If you take a look at the rules, the very bottom of the exception which defines which teleporters aren't KOS states:
My suggestion is that instead of making all vents KOS, change the rule to match those of teleporters. Specifically:
Vents which lead to areas that are KOS or areas that make a CTs job harder to keep track of you are KOS.
To the best of my knowledge, vents that are very clearly KOS are not affected by this rule change, and vents that are in the grey area such as those defined above will become not KOS.
Thoughts and discussion below is encouraged thanks!