Why is it immoral for you to desire, but moral for others to...

Why is it immoral for you to desire, but moral for others to do so? Why is it immoral to produce a value and keep it, but moral to give it away? And if it is not moral for you to keep a value, why is it moral for others to accept it? If you are selfless and virtuous when you give it, are they not selfish and vicious when they take it?