To answer whether bitcoin is a bubble, someone would need to quantify to what degree people of the world have lost faith in governments and other institutions. How much fear is there that the euro or dollar will crash due to high deficits and overprinting of fiat?
It is possible enough people have lost faith in world leaders to drive concern about crashing dollars/euros/economies to support the growth we're seeing in bitcoin, enough to make it sustainable.
no one in most developed countries cares about this. right now they're piling into bitcoin and alts to get rich and nothing else. normal people understand nothing about money and it's only greeks and cypriots who got a light schooling and even then they weren't subject to third world levels of debasement and inflation.
this is pure speculative mania.