I’m sure they deserve partial blame, but at least they brought in the sister. The people who deserve the lion’s share of the blame are the parents!
Consider: How many of the parents have used or are using contraception? How many of the children know about this? How many of the parents are divorced-and-remarried without an annulment? How many of them are receiving Communion on Sunday? How many of the parents and students don’t go to Mass on Sunday? How many of the students and parents haven’t been to Confession for years on end?
When people aren’t practicing the Faith—and the statistics show that that number is huge—one of the easiest ways to prove they are “loving” and “accepting” is to take the “who-am-I-to-judge?” route. How easy it is to “love” and “accept” someone who has never hurt you anyway!