What is the justification for holding the usurper liable for the diminution in value when paired items are separated and one part is destroyed?

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The correct position holds the usurper liable for the diminution in value because the defect resulted from his wrongful act. This is comparable to splitting a garment that suffers diminished value from the cut; if one resulting piece is destroyed, the diminution caused by the cutting must be compensated. This differs from price depreciation because here, a potential utility of the usurped item was forfeited, which is the source of the value depreciation, and this loss stems directly from the usurper's action, similar to causing the loss of sight, hearing, or reason, or dismantling a structure.