How can burning the Koran be considered a sin? The Koran contains lies, particularly a carefully constructed heresy which denies Jesus both that he was crucified and that he was son of God.
It is a sin against charity. The words on the paper are, indeed anathema to us as Catholics, however to burn this book, or pages from it, is to deliberately desecrate an object held sacred by those of another faith.
To do so is known to anger some members of that faith so much as to incite murders to be committed in revenge. By knowing this fact, to deliberately perform this act of desecration in a manner that had any chance of being discovered and thereby provoke such a revenge attack could make you (at least partly) culpable for any resulting violence.
It is a sin against the efforts the church is putting into ecumenical dialogue.
It is a sin against the efforts to foster mutual respect and co-existance between Christianity and Islam.
It casts grave scandal on fellow Christians. It causes non Christians to see us as intolerant and spoiling for a fight - not being examples of Christian Love and Respect.
Do we hear of St.s Peter & Paul advocating the desecration of the pagan temples and shrines in the cities where they preached and established their churches? -
NO!
They advocated taht the christians should change their behaviour, and lead exemplary lives of Christian Love and Virtue.
If I came into possession of a Koran, which I did not wish to keep and read (it can help to know what those we wish to evangelise believe), I would seek to give it back to the nearest Mosque and treat it with respect until the moment of hand-over. Admit in handing it over that you intend no disrespect and are handing it over as you understand that Muslems consider the physical book itself to be of inherent sacred value.
Regarding Christian texts and blessed objects which need to be disposed of:
I believe these should never be disposed of as garbage or with garbage. Any object which has been blessed for sacred use should be treated with the respect that that deserves.
A printed bible or other sacred text used for prayer or studying Gods word or Will should be treated with respect. Not thrown in the Garbage or recycling bin.
They should not be disposed of in a way that carried a high risk of profane use.
They should be respectfully buried or cremated. Objects containing metal or other precious materials should be recycled in a manner that involves the respectful dismantling of the object. (e.g. Chalices and Ciboria used for the Holy Eucharist must be melted down. The metals can then be re-processed and recycled. Ideally they should be re-used for new sacred vessels but that is not mandatory).