If you play little money like 3% of your monthly salary or even less and this amount is an amount you can afford to lose than there is nothing wrong with it. You are playing to entertain yourself.
If you play in an addictive way you without thinking about consequences for yourself, family and the ones around you then in this case gambling is totally wrong.
If you can't control yourself and have an urge for gambling you need to quit immediately and ask professional help. Google it, there's tons of websites which can help you.
That's what makes the difference. If you play for fun and use small amounts of money, there is no harm for you.
If you try to be professional and gamble daily with large amounts of money, it's a wrong career choice.
Going to be a professional gambler is not a wrong choice of career since you are shifted into that career. It is just going to be wrong if he is going to lose all of his assets such as properties, cars and well as he is not able to be a responsible person for his family. Then that is going to make gambling wrong because he is doing it wrong.