Some people gamble because they want to profit. Regardless of their skill or their understanding of the nuances of the game, that is a moral motivation (it might be unwise if they happen to be unskilled, or playing a game that is designed to defeat the player most of the time regardless of skill).

I know many people who gamble for this reason. Some are skilled, only play skill-centered games, and often come out ahead. Others recognize that they are not skilled, but are hoping to improve.

On the other hand, I know several people I consider rational to gamble with the understanding that they will never profit from it. I have a hypothesis as to why at least some of them do it. In a moral society, significant pressure is put on individuals to become wealthy through their own efforts. It’s a major responsibility, and the psychological impact when these efforts fail can be crushing. I think that some people gamble because they want to relinquish responsibility over their financial misfortune; they want not to be in control over the outcome of their efforts, because then when they lose, it wasn’t their fault.

If this is the mindset of anybody who gambles, I would say it is profoundly immoral. Viewed from that perspective, I would say that gambling is always moral if you take responsibility for your successes and failures as they come.