I don't think gambling is wrong but just don't be addicted. I love playing it, but not betting so much money.
You are right, gambling is not wrong because it was designed to give us fun and entertainment. But if we go greedy, then that is the start of a miserable life much more if we get hooked on gambling. So, better gamble for fun and entertainment with the money that we can afford to lose.
Concerning with hiw do we manage our self is the main concerned with this activity the more we engage our self the more we will possibly got attached letting us to forget everything and will start ruining our life and thats why most of the people around thinks gambling is really have bad results.