When you accept a member into your faction, you receive 1 XP.
When you deny someone entry into your faction, you receive 1 XP.
So what happens if you deny someone entry, and that same denied person asks again, and you deny that person again? Do you get 2 XP because you denied a person twice, or do you receive only 1 XP because you once denied that person entry before?
If it is the first option...isn't that something that can be abused? I mean, I could ask a random friend to constantly send a join application, while I constantly deny it. It would be a tedious measure, and it won't look pretty in the faction events (unless of course I am the only person that has the power to view the member list), but if I put my back into it, I could imagine getting roughly 300 XP per hour, and 7200 XP per day (Not saying someone would do this for 24 hours, I'm just presenting the numbers).
Golden Rule violation, admins will probably take measures if someone tries this. I remember a similar case with paying faction salaries some time ago...