I get why they would do that, to curb speculation, but it seems backwards to my intuition.

Just converting money back and forth should not be taxable. And if I make an advantageous trade with somebody, and a day later I make a disadvantageous trade, it should be a no-op. If you take it to the extreme, a market maker or an algorithmic trader makes thousands of trades a day, creating liquidity and determining prices, and they would be taxed a lot.

My gut feeling is instead you should tax people who use it as an investment and their long term gains.