I think Bitcoin can not be attacked because Blockchain technology is now growing and no one knows how Bitcoin was created. Only exchanges are attacked and this really does not affect Bitcoin
Of course it would affect bitcoin.
A successful attack, where someone steals huge amounts of coins from an exchange would be very bad for the value of bitcoin. Remember MtGox?
Such attack would erode peoples trust in bitcoin and crash its value even if it would be caused by exchanges bad security.