Also over 9000
Of course you can double spend it.
Take one bar. Cut it in half. Mix it with lead. Make two bars. Or whatever, ask a metallurgist.
The point is, I need to verify gold that you might give me. I need to verify Bitcoins that you might give me. Note as well that even with 51% of the hashing power, you still can't double spend forever. One chain has to be the true one in the end. All you can do is fool me for a while, just like with gold.
Being more widely accepted is purely a matter of history and chance. Who knows what will happen to Bitcoin's acceptance? Let's look again when Bitcoin trading is as old as gold trading is now to decide that one.