Same thing with any other position.
EVERYONE can have a motive to behave in an "unprofessional" way in a situation. Being homosexual doesn't make anyone "more likely" to behave in an unprofessional way.
You're being too general and discriminatory towards homosexuals.
The only other way is to construct a personal file on everybody in the country for intelligence purposes.
Then if you have a gay polieman or whatever the cases they are allowed on can be restricted to guarentee no unprofessional behaviour.