Meeting new people is not against human nature, humans enjoy meeting new people, the calls for a lfg flag show that people want to exp with stragers.

The reason people leve link with linkshell members is because it needs people to have the same leve, and its easier to manage that sort of thing in a linkshell party.

If there was a lfg system that people would want to use and grinding was a decent way to get sp then parties of strangers would be all over.

Also ffxi shows this when you have your flag up you get a party invite from somone you dont know and you accept it, this means the problem is with the system not humans