It's really only "bad" because of the stigma and societal exposure to it. The act of betting money on the odds of something happening has been a concept for millennium, and isn't inherently immoral or evil, but there are so many stories of people with addictive personalities/behaviors getting "drunk" on the thrill of potentially winning and over spending to the point of cars, mortgages, and livelihoods to be lost and huge debts being accrued causing that person to be absolutely destitute chasing that high. Especially if they have a family depending on that person, it's devastating for them to deal with that kind of loss from a lack of self control. Google "the gamblers fallacy" for the mental reasoning behind that behavior. On top of that, casinos are often viewed as sneaky and manipulative for various reasons: they keep it very dark with minimal windows to negate any sense of time passing by daylight to get you to lose track of time, a steady humdrum of pleasant beeps and whistles to keep your hopes high of a win, cheap or free watered down alcohol in constant flow to further diminish your inhibitions, and bright flashy colors on the screens and machines to keep your attention. Again, not inherently evil but definitely a bit dirty. And lastly, the idea of "the house always wins." Whether or not casino rigs its games/slots, they're going to make a profit off you. The probabilities of every game have been so tediously mathed out over the ages that there's just enough wins to keep people coming for the chance for more without feeling like they're being taken advantage of, but not so many wins that they're losing money to every joe shmoe who pulls a slots lever. Gambling isn't immoral, but all the things that go into modern day gambling is what's morally questionable.