And in unsupportive atmospheres, those inside have one move to make it to pressurized rooms or they suffocate. This also applies to space ship compartments, satellites, orbiting stations and planetary installations. Most fighter pilots and armored vehicles crews have the good sense to wear space suits, in case their ship gets penetrated. Pity those who don't. Full security and combat are provided by troops in space suits.
Internal security is handed over to troops without space suits and breathing gear.
BUT the outer space fighters MUST use blasters, ray guns and the like. Bullets can't fire in an atmosphere devoid of oxygen. Most larger space stations have redundant life support systems, and these are well-defended and armored. Small stations don't have this luxury, so if you an take out life support or the air supply, you've forced the defenders to wear space suits or else. AND without backup from a space ship, they won't be able to remain since their oxygen and temperature control will be used up.