For a given level of intelligence for a given person, it is possible to write a set of rules that make it appear that you have a reasonable chance of winning when in fact you don't. This is not a slam against the poor or the stupid, it is true across all levels of intelligence. The lotto gets a certain set of these people. Penny auctions step it up to the next level. Bernie Madoff caught another even higher level. (Yes, he committed fraud, but there was actually enough information for anybody paying close attention to figure it out with high confidence; his payout schedule was far too consistent, especially as the market started to drop yet his fund appeared to be immune.) No amount of intelligence will render you immune, though, there's always another layer of trick that would catch you, too, so let me emphasize again this isn't disguised elitism, everyone's vulnerable.
To the extent that the lottery appears to be disproportionately played by those who seem to be below the lottery's intelligence line, it is arguably a scam. And I do mean arguably, not that I have a proof. But I would say that if your response is that people know what they are getting into, I would submit that A: no, they don't necessarily really get it and B: would you be so blase if you were scammed by something a bit more sophisticated? It's easy to be unempathetic and be unable to imagine being fooled by the lottery's statistical games, but clearly it does in fact happen.
Is this proof of immorality or proof it should be shut down or anything else? No, I'm deliberately constraining myself to just the point above. Drawing it out further would take more logic and would itself be controversial. I just want to make the point that there is a plausible way to look at this situation and call it a scam without too much damage to the term.