Ah, mystery cults...you either love them or are emotionally traumatized by them. I can understand why the Romans were so against the Galli: Emasculated men in our manly society? Perish the thought! Then again the Romans were against anyone who didn't follow their way of life. For instance, the Bacchanates were too wild for the "sober" Romans; the cult of Cybele was clearly too against sexuality for the sex-crazed Romans; and Christians (they considered Christianity a mystery cult) were too peaceful and strange for the war-loving Romans. However, the cult of Isis seems to have been more or less acceptable; maybe it's because the worshippers of Isis weren't too crazy and out there for the average Roman's palate? Anyway, mystery cults involved rites of initiation that ranged from what we, at least would see as normal (the rite of baptism, for example, or maybe head-shaving in the cult of Isis (Golden Ass)) to the pretty bizarre, at least to us (self-castration for the cult of Cybele). What's the significance of the inductee (I believe Attis is doing this to himself) castrating himself? is this a show of extreme devotion to the Great Mother? On a personal note, I found this translation very strange, but kind of interesting.
Here's a link for more on castration if you're interested: http://en.wikipedia.org/wiki/Castration.