Truth, justice and peace: which is the "odd man out"?

Rabban Shimon ben Gamliel teaches (at Avot 1:18) that the world is sustained by three things -- truth, justice and peace. Which is the odd one out? 

My initial thought was that there was only one "odd man out", and that was peace. Take litigation, for example. When a legal dispute goes to court, the plaintiff and defendant both believe that they are in the right, or they wouldn’t go to the trouble of engaging in court proceedings. However, they know that there can only be one outcome. This outcome can be reached in one of two ways: either the court will rule in favour of one and against the other, or they will agree to settle their differences before the court gives its decision. Either way, one starts with two perspectives as to what is true, which give rise to diverse perceptions of what is justice (“mine” and “yours,” as it were). The dispute concludes with just one result, which both sides have to accept.

With peace, however, we have a different concept. There are not “two peaces”, since peace by definition only begins at the point where there are no opposing positions to synthesize. If what is called “peace” is not universally accepted by those affected by it, it is not true peace.

It occurred to me this morning that there is another possible answer: it is justice that is the odd one out. Truth is vulnerable to distortion and denial (we can infer from Avot 5:9 that it is of no use unless it is acknowledged) and therefore needs to be protected. God is described in Psalms as the eternal guardian of truth (Tehillim 146:6). Peace must also be guarded, hence the term "mishmeret shalom" ("guardianship of peace") that is recited in the text of the Grace After Meals and the congregational response to the blessing of the Kohanim. I am not however aware of any corresponding description of any protection or guardianship for justice. Have I missed anything, and does the fact that truth and peace need to be protected, while justice apparently does not, have any repercussions for our understanding of Rabban Shimon ben Gamliel's teaching?