No matter what religion do you belong its normal for us to commit mistakes because we are just humans by the way but its up on their decision if they obey your commit such mistake. For me its not a sin if you treat it as an entertainment but if you already risking all your money and it compromises your life and your family then it would be a very big mistake.
Nobody is perfect, every person makes mistakes, so if you consider whether gambling is a sin or not people still do it. I do gambling, but just for fun not to earning money for life, mostly people do the same. When you get addicted to it and ruin your life, that's why gambling consider as a sin.
You are totally correct, I fully agree with you dude. If people gambling for fun, no religion would defines this is a sin, because it is not for money. If they hunter for money, they may lose the family, house, car and so on. Which is a sin, even for non-religion people.