Bubbles are incredibly inefficient, they send huge amounts of very valuable resources (money, but also things like people, creativity, press attention) into situations where they are ultimately squandered. They are like wars, they can waste the promise of an entire generation, never to be recovered.

Nobody wants to see a collapse for collapse's sake, but there is quite a bit of social good in avoiding or deflating an asset bubble, be it in residential mortgages or late stage technology companies.