My issue with it is actually that it disproportionately affects the poor. I don't have a moral problem with it because it is, as you say, voluntary. I get that they aren't being forced. However, its effect is regressive and IMO any regressive net effect is bad for the economy. Think of it like this. If the reality was the opposite - that most of the tickets were purchased by the wealthy - that money wouldn't be reducing their consumer spending and hence aggregate consumer demand. If the poor and middle class buy the tickets, it will. To give a fuller picture of the economic impact, I guess we'd have to know how the money is spent. Yet even if it's is spent on a safety net for the poor, it's more or less robbing Peter to pay Paul, meaning it's pointless.
It's also why I don't like sales taxes. They're regressive, and worse still in the case of sales taxes, they discourage consumer spending even further by raising prices.
- wolf