My advice in this situation is that if you double or triple whatever you were comfortable starting with, you should leave the casino immediately.
It is easier said than done unfortunately. From what I see, the majority would just do "one more time" and "one more time" and on and on. Even if the gambler does leave the casino, he will be back sooner or later as he would keep on thinking about that $900 easy profit.
Well, it's a little thing called self control. If you don't have it yourself, you should work on it. But you don't have any right telling other people what to do by spouting bullshit about "right" and "wrong", or what God says or anything.
If you can't control yourself at a blackjack table, you definitely have no moral authority over anyone.