Fair point, but I don't think it's a particularly loathsome trash can. The price is low enough that only a small percent truly can't afford occasional tickets. And determined people find other ways to waste money. I had a friend who did a short gig working for a company that essentially sold magic crystals (jewelry, etc.). Shortly after starting she realized that the majority of customers were poor single mothers, and began to feel guilty about it. I'm not sure if the company deliberately targeted a particular class, but whether or not they did, what do you do about it, other than not participate? If you prove the company is a scam, you can shut it down, but there are ten thousand others like it out there. And there's the chance that the owners actually believe in their magic crystals, and that they're actually helping people. Not that that makes it legit, but it muddies the ethics.
I'm also assuming that most people only play the lottery occasionally for big jackpots, rather than as a regular money dump. If it's a periodic money dump than, yeah, there might be some ethical problems.