There is such a thing as a one-off incident (that is to say, ONE perpetrator and ONE victim), as opposed to the recent Post Falls scandal, which sounds like more of a plague of corruption/sodomy spreading among the boys there.
And there are different kinds of crimes. Some crimes are 100% reality -- they happened -- but didn't threaten anyone else, or at least not in the present day. In other words, there is no danger to the public good. Just like many human diseases are not communicable -- they are not transmitted from person to person. You can't catch heart disease, diabetes, cancer, etc. from a sufferer.
For example, if it came to light -- and to an SSPX priest's attention -- that Mr. A was abused as a child by Mr. B 20 years ago, and Mr. B is no longer part of the parish -- what should the priest do? Harm the parish by needlessly making the situation public (no public good was at stake), or keep it quiet? I would keep it quiet if I were him. After all, things like sex abuse tend to get people upset, concerned, scared for their children, and several people/families might leave the parish -- which would harm the parish. The parish might lose some volunteers, income, etc. And for what? It's not like the priest needs to publicly apologize, "take firm action", or something similar; he wasn't involved or even aware of the situation 20 years ago. And how can he take firm, decisive action? The perpetrator is long gone.
Advertising a scandal like this isn't good for a parish, you realize. Unless the common good requires it, there is no reason to air dirty laundry in public. In fact, I would say not parading dirty laundry around is the DEFAULT position. Making things public is the exception. But there are certainly cases where a good Catholic would NOT want to make a scandal public.
Scandals are eaten up by worldly people for some reason -- entire magazines make their living off the public's appetite for gossip and dirty laundry.
But Catholics look at scandals differently. For example, say you know about a priest who left the priesthood. It's a fact, publicly verifiable with evidence and everything.
Such a scandal is like a pile of dung. When you encounter a pile of dung, you can do two things: avoid it, or step in it. It's not pleasant, so why put it on a tray and parade it around, step on it, and/or smear it all over yourself? What good is accomplished by doing this? Few people will be edified by it, and no one will be protected by smearing the dung all over the place. So just leave it be. There is no harm in avoiding said pile of dung.
When it comes to scandals, the ONLY considerations for a Catholic is:
A) Is it true
B) Is it important for people to know -- does the public good REQUIRE it (is it necessary)
The following are considerations for worldlings but NOT for Catholics:
C) Is it interesting or titillating
D) Does it make me feel better about myself
E) Does it tweak my curiosity
F) Does it get me out the "funk" that is my own boring, dissatisfying life?
G) Does it provide a psychologically "healthy" escape/distraction from the problems in my own life?
Think about those points. Think of the average person who actually reads gossip magazines, and ask yourself if A and B really apply. Of course they don't. It's usually lies, and it certainly doesn't help the public good to know the sordid details of this or that failed celebrity relationship.
People buy those gossip magazines for reasons C) through G).