Ultimately, I think that a lot of ordinary social injustice arises because no one speaks out loud "Don't do that." Essentially, unwillingness to discuss social rules.
Saying "Parental Abuse is Wrong" is a useless Applause Light for most people.
Saying "It is not normal to be afraid of your parents, and not normal to be unhappy whenever you're at home" is more likely to be effective at creating good change.
Calling out Pat's sword privilege doesn't offer any explanation as to why Pat has the sword, or why Pat was motivated to stab Chris.
In case it isn't clear, I agree that calling out sword-privilege is only worthwhile if it reduces similar sword-privilege-abuse in the future. It's an empirical question whether (1) calling out privilege reduces abuse or (2) explaining why Pat has the sword is helpful to anything (figuring out what the abuse is, how to response effectively, or anything else). I suspect yes for both. But even if the answer to (2) is no, that doesn't demonstrate the answer to (1) is no.
Does it not seem odd to you to view the case of an unarmed person being stabbed by an armed assailant as an issue of social justice by default?
This is perhaps an unfair question, because I placed it in that context to begin with, but one of the things that's so maddening about the whole subject is how (for want of a better term) privilege is so privileged as an explanatory mechanism. There are certainly circumstances where it has merit, but it seems a ridiculous weapon of choice in circumstances where more appropriate explanatory mechanisms exist.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.