Interesting responses.
Our group has adopted a “Triad” attitude. If someone outside the group is wanting to come in then they must be known by someone in our original group. That person assumes the responsibility for the new persons.
The new folks are answerable not only to their “sponsor” but everyone else.
When SHTF and everyone gets here we then set up the “Triad.” I will be one of the members. The persons at large will elect another member. Then myself and that newly elected person will pick a third member.
Once all that is settled we will revisit our policies and rules.
Will we turn away strangers? If they can not be producing members of the group (doctor, nurse, carpenter, person that knows about stuff that grows wild) then we will give them some supplies and send them down the road.
Bottom line is that the Triad will make these decisions.

There again, nothing is perfect.