100/week is 5200/year. That's probably the difference between making ends meet and being always in debt for a lot of households - the median us household income is about $50k and we're talking 10% of that. That's a huge difference for the median household, and likely pretty catastrophic for the bottom quartile.
Which arguably is as much a problem with income inequality as anything else, but the point is, gambling exacerbates existing social problems.