Nic Carter, a general partner at Castle Island Ventures, has raised concerns about the potential impact of quantum computing on Bitcoin's security. Carter highlights that approximately 6.7 million BTC could be vulnerable to quantum attacks, posing a significant risk for long-term investors. He emphasizes that the cryptocurrency community may be underestimating this threat, which could lead to panic if quantum capabilities advance before adequate defenses are established. Transitioning to post-quantum systems is expected to be a complex and risky process, potentially altering the risk-to-reward ratio for Bitcoin.