Don't want to be too critical of my RC friends, but I have to wonder how this group measured up in the first place.
I'm no expert, but I'd say it was a result of what I said above about the Alinsky groups. When these groups were in their ascendancy, the Church was in the process of becoming infiltrated by some VERY leftward-leaning priests and bishops, thanks to a socialist as a papal nuncio. (European politics, remember?)
At any rate, these "moles" were moved into the Church's heirarchy over a period of years, and gradually they eased their policies into place. The Vatican does not "vet" priestly candidates, but it ordains bishops on the say-so of various advisors. If the candidates are protoge's of the leftist cardinals, their secrets will be hidden from the Pope. This, unfortunately, does not invalidate any Holy Orders imparted in those ordinations.
So this is how these bums got in, got established, passed on their propaganda, encouraged and condoned the leftist tilt of many of the Church's outreaches during that time. The groups have achieved a certain "respectable" crust, but their roots run deep into the Alinsky IAF groups.