For the same reason he dislikes gold I suspect. He benefits tremendously from the status quo dollar fiat system. He has stated it's a critical ability for the Fed to be able to step in and do what they did eg in 2009, acting as a supposed lender of last resort. A de-centralized money system would end or severely hamper that. Buffett has also frequently stated that he strongly prefers goods that produce (using everything from farmland to owning Coke as examples, as opposed to gold which doesn't produce, but rather is properly a store of value). From everything I've read over the years, I would say Buffett strongly prefers that central banks be able to step in and inflate / devalue currencies when it's deemed necessary. In a world of dominant bitcoin-like currencies, that ability pretty much goes away.