Just my opinion but in lowsec, the plexes make a good point for pvp, unlike nullsec where allot of the actions happen at the gates, so I personally wouldnt want to block non fw players from entering, if you block neutrals/pirates, they will join a side just to enter then awoxing will be another issue.
ppl in the same faction already enter sites to score some kills, trust does not come fast, that wont be something new, and by commiting players to join a side will only make FW more challenging, and thus, less of a farm place or passible to be controlled by one side due to the nature of nowadays neutrals, wich is in my opinion, to score some easy kills.