There may be many differences between a Bitcoin investor and a gambler but I will point out one similarity between a Bitcoin investor and a gambler is that both gamblers and investors are in risky business. An investor can easily refrain from investing if he wants and can invest in the market as per his will but a gambler cannot easily refrain from gambling.
There is definitely a difference between a Bitcoin investor and a gambler. A gambler can lose all his money anytime he gambles but a bitcoin investor never loses his whole money. Because we all know that Bitcoin is volatile, even if the price of Bitcoin goes down, it rises again quickly which we constantly see in the cryptocurrency market.
But why do many people still lose money when investing in bitcoin and even lose it all? When you take profit or someone takes profit, it means someone will buy your high priced bitcoin, and when you win, someone must lose. That's how financial markets work and investing in bitcoin is no exception , so I won't agree with you that no one will lose money investing in bitcoin. Whether or not investing in bitcoin is profitable depends on the mindset of each investor, not bitcoin. In my opinion, the line between gambling and investing is knowledge, if you invest without knowledge then you are just gambling.
The similarity you find between Bitcoin investors and gamblers is that both involve risk. Yes, that's right. But I think gambling involves more risk than investing in Bitcoin. Have you ever seen someone who lost their entire money investing in Bitcoin, but there are many cases where they lost their entire money due to gambling addiction and even sold their house. Investing in Bitcoin for a long period of time can expect profit from it but can never expect profit from gambling as it depends entirely on luck.
Basically, risk always exists around us because no one can predict what will happen to us, not only in investing and gambling are there risks. And to be able to control or avoid risk requires knowledge, knowledge is still the line that makes the difference between investing and gambling, IMO.