Your question is not clear with regard to what information you are actually seeking. There are at least two major issues to consider here, and in my ignorance of the situation, there are probably many more. One of those issues is a cultural one. As a "westerner" I realize the culture finds this acceptable. I fear that it is acceptable for the wrong reasons--let's marry the girl child off because she's an extra expense, and she cannot add to the family name rather than let's find her a protector for life. However, that assumption is made with limited knowledge. On the other hand, there is a humanity issue here, and I can never accept in any means that it is okay for a child to be married and engaged in sexual relations even before some of them reach sexual maturity. How is that really any different than child predators?
I am not certain as to where you are searching in light of "argumentative info." I am not sure I can find, or want to locate, evidence which suggests that this is acceptable or a good thing. This might be an instance where moral relativism could be wrong on this. I think the interesting element would be in a post- Taliban setting where Afghanistan is now, would more practices of the West be adopted? In this understanding, how would the perception of child's marriage be seen? I think this might be an interesting dynamic which will have to be assessed over time in the Afghani social and political discourse.