Don't know about you, I've been 100% loyal to Advent V, without any problems.
But I do agree, it's too easy to join and leave guilds. The reason why it isn't a "huge thing" when players switch guilds, is usually that the guild they switch between are friends. I consider veteran tower takers that were infamous switched guilds to another major tower guild a big change. Like, lets say if DarkDeathAngel was known by Chain of Memories, Ximtra, Advent V, Rebellious, for being a good tower defender from Project Soul, and he switched to Chain of Memories permanently, it would make for big news in that community of tower takers.
Dunno, that's my little two cents.