i think so too, for Christians, if for fun or charity(in some countries all casino winnings are country's, like Finland, they use the money to pay welfare to poor people), it is not a sin.
if people don't work, just only wanna be ridiculously rich, it is a sin, working for life is necessary thing.
for muslins, gambling is 100% a sin, but it is still very popular in muslin countries, like malaysia and indonesia.