Bitcoin's meteoric rise in price this year is backing people into two camps: the deeply suspicious and the incredibly enthusiastic.

Andrew Left, a bitcoin critic, and Tom Lee, an all-in admirer, squared off Wednesday on CNBC's "Fast Money."

Left, of Citron Research, is a noted short seller who likes to find stocks that he thinks are overvalued and due for a fall, and bitcoin has been a big focus of his lately. This summer, Left outlined his argument against the Bitcoin Investment Trust, a fund run by Grayscale Investments that is supposed to track the cryptocurrency's meteoric rise. Left says bitcoin is exorbitantly priced relative to its underlying value.

But Lee, of Fundstrat Global Advisors, has said he sees bitcoin going to $25,000 in five years and possibly $55,000, and he has endorsed the Bitcoin Investment Trust, calling it an "attractive buy."

At the time Left revealed his bearish call, bitcoin was trading hear $4,775. It is now trading around $5,695, a gain of 19 percent in less than two months.

The Bitcoin Investment Trust is up 456 percent for the year.

Left said on Wednesday that Lee's call of $25,000 is "irresponsible," and that he's giving investors the idea they can get rich fast. "We don't know what bitcoin is right now," he said. "It has to find its identity." He questions whether it is a currency or an asset.

Lee said on CNBC that buying the Bitcoin Investment Trust is a way to capture most of the potential rise in bitcoin with more liquid exposure and he admits bitcoin is a "very risky" investment in and of itself. He agreed investors should only allocate a small amount of their money.

Fundstrat's Lee, a former chief equity strategist at JPMorgan Chase, sees the cryptocurrency as a store of value like gold, and investor interest will push the price up. "I unequivocally think bitcoin is your best investment," he told "Fast Money" last month.

"I wouldn't want investors to put 100 percent of their money into bitcoin," he said. "I actually think it's still early," adding bitcoin wasn't a bubble as he could see.

Though bitcoin is not widely held now, efforts by the Chicago Board Options Exchange to offer bitcoin futures trading by early next year may help increase ownership, he said.

His view is in stark contrast to that of his former boss, JPMorgan Chase CEO Jamie Dimon, who has called bitcoin a "fraud," but says he sees value in the blockchain technology that supports it. Many banks have been exploring the use of blockchain, a digital accounting ledger that lets users follow a chain of transactions, for settlement and other uses.

But other prominent bankers have been less critical. Goldman Sachs' Lloyd Blankfein has said he hasn't made up his mind about bitcoin though the bank is exploring how to trade it in response to inquiries from clients.