These are remote access gates - they are designed to be accessible by passengers without a member of staff being in attendance. This does not mean that you shouldn't expect a member of staff to be there at certain times - rush hours for example. But it would be entirely unrealistic to expect staffing throughout an 18 hour day, seven days a week.
The approved planning application makes it clear that the gates will be accessible from September whenever trains are running. From September TfL take over running local stations and Oystercards come into operation. TfL have made it abundantly clear that they will staff local stations throughout the times that trains are running i.e from c6am to after midnight.
When TfL take over, problems of access will ease. In the meantime, we need a degree of responsibility from Southern to their passengers.