This article originally appeared in the Motley Fool.

It's been a rough start to 2018 for bitcoin (BTC-USD) and most other cryptocurrencies. Thanks to a steady stream of negative news items having to do with regulation and other matters, bitcoin has lost more than 38% of its value so far this year.

Adding fuel to this fire are comments by several investing and financial industry heavyweights, which have mostly been quite negative about the fast-growing cryptocurrency market. However, two bitcoin billionaires are firing back.

2018 hasn't been so kind to bitcoin. GETTY IMAGES.

Warren Buffett, Carl Icahn, And Jamie Dimon Have Said Some Pretty Harsh Words About Cryptocurrencies

Several major investors and financial-industry professionals have spoken out against bitcoin (BTC-USD) and other cryptocurrencies, generally predicting a big decline.

Warren Buffett, for example, recently said that "I can say almost with certainty that they (cryptocurrencies) will come to a bad ending." While he said that he'd never short them because of the unlimited loss potential, he did say that "If I could but a five-year put on every one of the cryptocurrencies, I'd be glad to do it..."

Billionaire investor Carl Icahn recently called cryptocurrencies "ridiculous," although he admitted that he doesn't understand them well.

And J.P. Morgan Chase Chairman and CEO Jamie Dimon has backed off from comments that bitcoin is a "fraud," but has also said that cryptocurrencies would never be a major competitor to the dollar.

In addition, investment bank Goldman Sachs published a note recently that said most virtual currencies would eventually crash to zero.

These Bitcoin Billionaires See Things Differently

Tyler and Cameron Winklevoss, the twins who famously received a large settlement from Facebook after claiming that Mark Zuckerberg had stolen the idea from them, are widely regarded as the first bitcoin (BTC-USD) billionaires. The twins invested heavily in bitcoin well before 2017's rally and co-founded the Gemini cryptocurrency exchange.

In a recent CNBC interview, Tyler Winklevoss said that the negativity of Buffett and the others was a "failure of the imagination." He went on to say that "as you get older your brain loses its plasticity at some point and you get wedded to the frameworks that you have."

Winklevoss also said that when you're taught for 60+ years that money is only in paper form or in the form of precious metals, it's hard to unlearn this concept. In other words, the Winklevoss twins believe that money is in the early stages of transitioning to digital form, and this concept might be too much of a stretch for the aforementioned critics to understand.

Cameron Winklevoss also gave a lofty prediction for bitcoin's price, saying that the digital currency could be worth 40 times its current value one day. "We think regardless of the price moves in the last few weeks, it's still a very under-appreciated asset," he said.

Why Will Bitcoin Be Much More Valuable In The Future?

The Winklevoss twins think that one driving force that will propel cryptocurrencies higher is the massive unbanked population around the world -- that is, people who are not currently being served by the global financial system. "If you go to Africa is there J.P. Morgan branches opening up there and banking the unbanked?"

In addition, the twins pointed out several key flaws with the current global payments system. For example, they pointed out that international wire transfers take so long in many cases that you can transfer money quicker by flying on an airplane. And that many functions of the financial system are only available from 9am-5pm, Monday through Friday. A system based on cryptocurrencies could solve both of these problems and more.

Who's Right?

Obviously, we won't know which side is right until bitcoin and other cryptocurrencies actually become a significant portion of the global financial system as the Winklevoss twins predict, or until cryptocurrencies collapse as the naysayers believe will happen.

Both sides certainly have valid arguments. On the negative side, there are many challengesfacing bitcoin and other cryptocurrencies that would need to be overcome before they could become mainstream payment mechanisms. And to the Winklevoss twins' point, Buffett and Icahn openly admit that they don't understand cryptocurrencies, and Buffett has been very wrong in the past when it comes to avoiding businesses he doesn't fully understand, such as Amazon .

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John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Matthew Frankel has no position in any of the stocks or cryptocurrencies mentioned. The Motley Fool owns shares of and recommends Amazon, and has no position in any cryptocurrencies mentioned. The Motley Fool has a disclosure policy.