Kithraya is right. The big problem is the fact that items are accessible with or without and enchanter. If the enchanter could DE the corpse of the boss to get a shard instead than this would be a non issue. The fact that the Enchanter is taking money out of the hands of the rest of the group if they are present is what annoys players. You can see situations arrise in some groups if the enchanter was allowed to keep all non need items. People would stop inviting them into groups so that they can at least get some money selling to vendors. Im not saying it's right or wrong to do this but it would happen.

As for giving others my herbs if i gather in an instance, if someone wants them sure ill give them away, the ammount of herbs i get from an instance run is insignifican compared to my normal farming. Doing an instance slows my herbing down, i get barely any alchemy ingredent for my time in there. I could flush all the herbs i have ever gotten in an instance down the drain and it wouldn't really matter. Enchanters can't say the same thing. Not really sure if thats and argument for or against them keeping all the ingredients but it's still true.