The words “notorious” and “manifest” imply apostasy and sin which is commonly known amongst people. The ordinary man or woman of no “note” (cf. notoriety, etc) cannot really cause much scandal (a trap, a temptation, a stumbling block…if I still remember my Greek!?) amongst the faithful, as they are not known widely (except, maybe, amonst a few locals, the immediate family, etc). To make something manifest is to reveal something, or to make it well-known. Canon 1184, therefore applies more so to a) Churchmen of high rank and / or b) famous people / politicians. It is they, by their actions, that can have detrimental effects upon Christ’s faithful. It is by our standards that we shall be judged - the mighty and the in/famous have a greater deal to account for that the lowly and discreet.
From what I have read Stephen Gately had not spoken to his parents (who are always referred to as “Roman Catholic” in the press - as if to expose a difference between him and them) for many years (because of his homosexuality). They did not even know that he had entered into a “Civil Partnership”. It does seem, though, that he was reconciled to them recently, but probably not to their faith - seeing he was still in a highly irregular relationship contrary to the faith and morals of the Church. I have also read that Stephen Gately was a follower of “Chakra” (whatever that is) and it’s connected eastern mysticism. If I were ever to take up eastern mysticism, fall out with my family (as they could not accept a lifestyle of mine because of their Catholic faith), and entered into a situation that effectively excommunicated me (by entering a mockery of married life - well abouve and beyond any mockery which the divorced and remarried might be responsible for) then in all conscience I would be, and would consider myslef to be, apostate.
So this case has the notoriety which fame can amplify, coupled with apostasy and manifest sin.
It is plain and simple - the Church should not have condoned or sanctioned this requiem. In doing so it is my opinion that some scandal (trap / stumbling block) has been put before the People of God - some of whom now might think that the hierarchy approve of gay lifestyles. We Catholics believe in the sacred nature of our conscience (“The Aboriginal Vicar of Christ”, as Newman put it) - if someone, in all conscience, decided to live a life contrary to the Church’s teaching then we may, with some delicate confidence, assume that the man / woman in question would not have wanted to be buried according to the rites and rituals of the Church. To bury someone in such a state, let’s say to keep religious relatives happy, would be to denigrate his / her conscience - thus scandalising the Church’s own teaching that we have free will, and we must (above all else) live according to our conscience.
I wonder whether the Holy Father would have sanctioned this requiem? If there is any scandal involved in this case - it is not Stephen Gately who caused it, but the hierarchs of the Church.