~snip~
Yes you are right. I am also think with the same way that gamble isn't any bad think. Yes it's convert to bad when one person got addicted on it . I think not just gambling but over-indulgence has a bad effect on everything. So in this way gamble should be in self control and also it's purpose should be only entertainment which already mentioned by op.
I think it doesn't matter whether a person gambles for fun or for profit as long as he gambles responsibly, I believe there will be no issue ahead. The problem with people who gamble for profit is that they failed to set up a limit on the fund they have to spend resulting in spending money that is allocated to households expenses. There are lots of cases where a gambling have to sell everything in order to recover what he has lost because of being irresponsible while gambling.