Understanding ecumenical dialogue from an absolutist's persective

The following quote is drawn from an excerpt of a transcript of an interview conducted by the ABC's Tony Jones with a Catholic bishop, Mark Coleridge, on Wednesday:

TONY JONES: Well, he’s saying that there are problems with ritual and superstition in other branches of the Christian church, and he seems to be extending that to Islam and Judaism if you look at it by extension.

MARK COLERIDGE: If you look at – indeed, if you read Dominus Ieusus, what you will see is that it proclaims anew what Christianity has always said from day 1, and it's this: that Jesus Christ is the world's only saviour. There's nothing new in that. It wasn’t just Ratzinger who said it. This is a fundamental belief of Christianity. In other words, Buddha, for instance, and Mohammed are very great religious teachers, religious geniuses, but they are not the saviour of the world. So that what Ratzinger is determined to speak against - and I think this will be true of his pontificate - is what he calls relativism. In other words, your opinion and my opinion are equally valid or invalid. There is no such thing as truth. There is no such thing as absolute truth...

TONY JONES: But isn't that a huge problem, though, when you're trying to deal with other religions that believe they - as the Catholics do - have the absolute truth, and you can't argue with them that their version of God is different than yours and therefore not as good?

MARK COLERIDGE: No. Tony, anyone who's been involved seriously in interreligious dialogue would say that the only real basis for true dialogue - not just having a garden party, but true dialogue - is that I speak from the position of my belief and you speak from yours. We don't sort of assimilate one to the other. That's no basis for true dialogue. Dialogue presumes difference. So what Ratzinger spells out in a thing like Dominus Ieusus is the basis from which Christianity enters dialogue. It doesn’t foreclose dialogue; it makes it possible.

"Dialogue presumes difference...It doesn’t foreclose dialogue; it makes it possible."

I can't see how productive dialogue is possible if one holds that: a) there are absolute truths, b) one's own interpretation of those truths is absolutely correct, and c) one's dialogue partners' interpretation of those truths is fundamentally misguided and incorrect.

It seems obvious to me that if one is to have productive dialogue, both parties must agree to disagree on the points of fundamental difference thereby making those points of difference irrelevant to the outcome of the dialogue. In which case, interfaith dialogue can proceed irrespective of whether one holds a relativist position or not.

Indeed, I would think that relativists can more easily participate in such a dialogue, if only because relativists are not forced to defend irrational and logically indefensible positions and would naturally seek to base the dialogue on points of shared belief.