The problem with cremation is that it is rather...Gnostic/Manichean in its original intent.
The body is good and natural part of our complete being, not an evil shell that holds surrender our self. To burn it as if it were something of no consequence seems to reject our Christian understanding that the physical isn't evil or an illusion but benevolent, complete, and real.
Of course, that isn't the reason why today humans practice cremation, although I still take some issue to it. However, the fact that people are sadly sometimes killed by fire, acid, or some other dissolvent shouldn't be a barrier either. True, those things are involuntary, but the effect remains the same.
Not to mention that the body will naturally decay anyway, reducing even bones into dust.
I suppose the question is this: are you denying your complete being if you choose to be cremated? I err on yes but I don't deny exceptions that could possibly exist to the rule. I find it disturbing that someone who simply choice to burn away part of who they are. Yes, your body would eventually become dust, but why hasten the process? Are we so abhorent of death that it has become so unsightly? It is a natural part of life, and in order to live a truly human existence, we need a physical form, and I cannot reject mine.
When I die, I hope to simply have my body thrown into a shallow grave. No box, no urn.