Because its the proper scale for these things. Ask your math teacher tomorrow in school.
Ok, still looks like a bubble in log-scale.
Did the move from 5 to 10 look like a bubble? Maybe while it was happening it lookid like a bubble, but a few months later when the price remained close to 10 it no longer looked like a bubble, just a move from the old price to the new price. If the price levels out for a few months we will then know this is not a bubble, it is hard to tell while we are in the midst of the run up whether this price will be sustained.
Proudhon is a troll. I wouldn't waste my time responding to him.