I don't think the player should be penalized at all because the player is punished by proxy just through guilds not wanting to recruit them and risk penalization
I think the guild itself should be penalized, falling in line with the points system that was discussed in another thread

Players should be freely allowed to join any guild, but guild leaders should be considerate of who they are recruiting and that in itself should eliminate the "noob recruiting" strategy (which is anti-competitive, boring, non-interactive, just stupid altogether)

And I know everyone's concern is then, "OMG, BUT HOW DO WE HOLD TOWER WITHOUT NOOB RECRUIT?"
Consider the fact that every guild will be held to the same standard, it applies equally across every guild