Why do people see "doomed to failed, because it's not already big", while I see "Has tremendous growth potential, because it's not already big nor the defacto world currency".
Because they're either trolls or ignorant, usually both. Obviously we can see the potential in bitcoin and the opportunity for both growth and profit so we see it as a worthwhile investment, but others don't. Some people thought it was a get rich quick scheme and it didn't work out for them or they lost a lot of money and now they're pissed so they become aggressive and cynical.