I am not sure how gambling can be taken up as a profession. Gambling is something that is purely dependent on luck. Also, you need to remember that there is a house advantage, which lowers your chances of a win. That means that even if you go for a 2x bet, the chances of your win is not 50%. After implementing the house advantage, it can get to anywhere from 45% to 49%. And that means that in the long term, you are likely to lose money. If you bet 100 times, then the chances are that you may win 45 to 49 times and may lose 51 to 55 times. In the end, you will be left with a monetary loss.
It applies for non pure luck based game such as poker and sports betting where gamblers are able to use some knowledge, analysis to gamble. It is proven already that there are many professional poker players who use poker as one of their main source of income. In this situation, those poker players are using gambling as a profession.
It wont apply to any games which is luck based game such as dice, slots, roulette, etc because gamblers wont be able to push their luck by using strategy or knowledge or even skills. So gambling such kind of game should be used for fun purpose only instead of profession.