you dont understand that you dont help the community if you make certain items worthless. i might throw away a few things that others could use, and so do a lot of other "rich" people. but if we would also place them on mp, or even donate them for free, "poor" people wouldnt be able to sell the mediocre items they might find at all. and we all know that it can take ages until you find something thats worth a bit more, so many people rely on their 1-10fg sales.
it helps a lot more to tell beginners what they can sell, so they can make fg to get their own gear.
with this information for example:
http://forums.d2jsp.org/topic.php?t=37296033&p=244014257...you can easily make at least 50fg each climb.
then just lvl in catacombs to 65+ and do some treasure chest hunts (create group and engage

walk around and hope for treasure chest

if mobs spawn: run / if treasure comes: grab

repeat) which gives also people who are not able to kill a single mob on their own the possibility to get gg items.
if you sell your gp too, you should be able to afford ~50ee items for every 10 levels on your second or third climb already.
people always worship items they "worked" for and found themselves much more then donated stuff. and if you get everything donated you will loose interest pretty fast, so that also doesnt help getting new players to the game.
I understand what your saying, the only thing I disagree with is that a few people that would actually use this feature would NOT imbalance the mp system at all. Thats just my thoughts on it. People will still buy items, as it would be cheaper than having a vault, but this does make it easier in the long term.
At farsides comment, you could very well be right that this is not needed at all, I just tried to think of a way to give back to the community after seeing several donation threads shot down. Whether or not the idea is approved does not matter to me, its an idea and I didnt expect it to go anywhere. Im just trying to find something that works for everyone.