You CAN disenchant (aka DE)a soulbound item, but only when it is YOURS. Soulbound items are usually questreward items and/or boss drops. You can tell if and item will be a soulbound item by looking at the top right corner in the item discription. On the item description it will say either "bind on pickup"(aka BoP) or "bind on equipped"(aka BoE). Soulbound items are the "bind on pickup". However, to get around not being able to DE  other players soulbound items, an enchanter can do the following. When running a dungeon/instance with a group and no one needs a bossdrop that's BoP, the group can agree for the enchanter to roll need and disenchant the item. After the enchanter DE's the item, the group can roll(type /roll) for the DE reward. Then the Enchanter can pass along the DE'd mats to the winner of the roll.