Money runs gambling. It gets transferred from a point to another. From the poor to the wealthy, from the wealthy to the poor.
Let's first talk about how the poor gives the money to the wealthy.... They allocate a huge part of their money (which isn't a lot in the first place) to gambling thinking that this would be the quick fix to their problems. This is how they give the money to the wealthy in this case the casino owners.
But the money can also go from the wealthy to the poor. If the tax from casinos gets collected by the government and is used effectively, it can help a lot of those in need. The money can be used to improve infrastructure, education, healthcare and etc.
If there is a tax... However, the fact is that gambling is as much a part of the economy as any other. In economics, money always goes from the poor to the rich. In the opposite direction, money comes in isolated cases, for example, as the accidental winnings of individual poor gamblers, for example, in a casino. Improving public infrastructure through taxes is not an influx of money from rich to poor people. It's just a handout, kind of like benefits. There are trends in the distribution of wealth (you can read Stiglitz, Piketty), which indicate a continuous increase in inequality in the world over the centuries.