This would be my take on the subject, admittedly adapted from a compilation of my real world views and the needs of the game.
Gambling is first of all an activity that is ripe for corruption and illicit involvement by criminal elements. Large scale gambling more so than small scale gambling. Therefore when large scale gambling is seen in game (lotteries, races, contests, casinos, etc.) then there is a good chance that it is supported by some sort of corrupt or evil society (thieves guild, church of vice, etc.). PCs who get involved in such activities may find themselves caught up in these elements.
The moral argument against gambling (both large and small scale) is that it involves taking money from one participant and giving it to another. You only gain by someone else losing. This may or may not violate certain religious strictures. A good aligned church which is more focused on fighting and killing evil creatures may have no real problem with an occassional toss of the dice. A good aligned church focused on honesty, fighting poverty, family values and the like may have real problems with any gambling.
In Kalamar, my campaign world of choice, I would guess that if I was to introduce the subject of gambling, The Home Foundation (a church focused on family), The Courts of Justice (church focused on law and order and fighting crime), The Church of Life’s Fire (church for farmers) would be some good churches generally opposed to gambling. On the other hand The Temple of Stars (church of travelers) might be a goodl aligned church with no problem with it while other good churches probably are fairly neutral on the subject. On the other hand, The neutral churches of both the Mathmaster and the Strategist might see some value in trying to win a game of chance through strategy and the Evil churches of the Vicelord and the Battlerager would actively encourage gambling because it perfectly fits their tenets.
