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Responsible gambling I think means that we must only gamble what we have spare and aren't too worried of losing it. People spend money on movies don't regret watching it right? Similarly people gambling should not regret losing it.
Spending on watching movies is a perfect comparison, imo, I'm using it too. Take the ticket price. This is exactly what one can easily afford to lose in a week/month of gambling, depending on how often they buy movie tickets. For some people(and I was one of them many times) even once per month is too expensive. Such people to be responsible gamblers should spend on gambling accordingly: less than $10 per month.