My understanding of 2 john is that John is addressing a congregation of believers. The warning about inviting the person into your house I believe is better understood to mean do not invite the person to teach and preach in your Church. In essence, don't let known false teachers have the pulpit. I saw this once at an old SBC church I attended in college. One of the Sunday school teacher allowed a Muslim to come and speak to the Sunday school class for the purposes of getting to know what Islam teaches. The guy only only served to cause problems among the younger believers.

Though I do respect families who would not want to invite young Mormon missionaries into the home for a meal and a discussion on salvation, I do not think John's words are prohibiting such a scenario.

Fred

"Ah, sitting - the great leveler of men. From the mightest of pharaohs to the lowest of peasants, who doesn't enjoy a good sit?" M. Burns