The best argument against the church engaging in social justice is that there ought to be no such justice that needs to be modified by the word "social". As Hauerwas said (somewhere) "Justice is justice". In other words, something is either just or it isn't. The language of "restorative justice" or "retributive justice" or "social justice" pits justice against itself. If retribution is just, then it is not "retributive justice" that has been carried out, but simply justice. If retribution is unjust, then justice has not been done no matter what modifier we put on it.
As for social justice, if there is a form of justice that is not social then there is no triune god.
Something similar holds true for love. Christians -- including myself -- have a habit of talking about "self-giving love". But what other kind of love is there between persons? Because of the story of God's relation to humanity, love is self-giving. Talking about "self-giving love" prolongs our illusion that love can also be something other than self-giving. It can't, and the sooner our language reflects this the sooner we will realise that we live lives that have very little use for the word "love".
And on that note, an early Happy Valentine's Day to everyone!
ps - This phenomenon is also true of the gospel. In a recent blog post, Scot McKnight pitted the "soterian gospel" against the "story gospel". But in the letter to the Galatians -- the letter that was excluded from McKnight's list of gospel sources -- Paul says that there is only one gospel, though others have distorted it and thus have turned it into no gospel at all. Again, the point is simple. Something is either the gospel, or it is not. If the "soterian gospel" is not the gospel, then it is no gospel at all. If the "story gospel" is the gospel, then it does not need the word "story" before it. That's simply a kind of re-branding; a marketing trick that has no place in the work of theology.