The point of the donation is that you've given up control. If I give you 1 share of Facebook, it is now yours to hold or sell. So, you are responsible for any g

The point of the donation is that you've given up control. If I give you 1 share of Facebook, it is now yours to hold or sell. So, you are responsible for any gains or losses on that asset from that point forward, which is why the value at the time of the donation is used.