Whether the gate is locked or not, whoever uses the road still needs to stop to open, so locking it does not contribute to a greater risk in that regard. Believe me, a locked gate is a deterrent, whether it is believed or not.
Same argument will apply to your house. Why bother locking your front door if a burgular can break a window or get inside in another way, yet it is a no-brainer that the door must be locked. You will never stop the guy who wants to get inside at all cost, but opportunity makes the thief if it is too easy.