The biggest difference between futures trading and gambling is that in futures trading, you can control the outcome, whereas in gambling, you cannot. Futures trading involves speculating of the future price, while gambling is a form of entertainment. With futures trading you do need to consider a lot of factors like maket trend, analysis data and make correct trading decision. In gambling all you do not need any kind of skills, comparing the two does not make any sense. It is incorrect to assume that they are the same, as they are not.
No one can actually control the outcome in futures trading, that is a wrong statement, what you can do in futures trading is predict the outcome more accurately with the help of market knowledge, experience, and fundamental and technical analysis, and that is what makes it different from gambling because you don't have a chart to read or a team or a project to analyze or a past to check when it comes to gambling, it's pure speculation.
The outcome of both of course isn't guaranteed, even in futures trading, you don't win all the time, if that were the case, there wouldn't be millions of dollars getting liquidated every now and then, that happens because people choose the wrong sides and market moves the other way, but it is just that if you are careful and have a lot of experience, you will have more chances of getting profits.