Being a bubble does not mean that underlying idea or company is worthless (for example .com bubble), but just grossly overpriced. Since bitcoin generates no income on its own and have no underlying organisation (like countries for fiat) it technically speaking will always be speculative. And as speculative asset it will always be prone to bubblement. I think its good and healthy for bitcoin that there are people stopping it from uncontrolled growth. I don't believe bitcoin will burst but from technical point of view I understand calling it a bubble.