Gambling is not mentioned in the Bible, however indirectly it is looked at as sinful because it is an irresponsible way of dealing with money, it takes many losers to produce a winner. The Bible does state that a man be foolish in being irresponsible with his money, and most anything called foolish in scriptures is sinful.
God loves those who believe and those who do not and the same goes for me, you have no choice in this matter. That puts the matter of total free will to rest.