Kevin O’Leary, known for his role on Shark Tank, has declared that altcoins are no longer viable investments, emphasizing that Bitcoin and Ethereum are the only cryptocurrencies delivering significant returns. O’Leary points to the emergence of legal stablecoins, which he says have reduced Bitcoin's utility as a payment method. Additionally, he highlights the impact of the upcoming Clarity Act, which has left many tokens in regulatory uncertainty. According to O’Leary, most altcoins lack substantial use cases and cannot match the credibility of Bitcoin and Ethereum.