What is so dangerous about being allowed to send mail to our mates in our Free Companies without being on their friends' lists?
The post you're replying to specifically says we should be able to send mail to other members of the same free company without first friend-listing them. That would let you mail to alts (edit: providing they are in the same FC) without friending them but would still keep gil sellers from mailing you. Unless the gil seller is in your FC, in which case they should either be kicked or told to improve their account security.