Because 35 percent goes to neither winners nor losers, the real cost of the lottery is that you win less often and the prizes are smaller than would be the case without a government monopoly. If government allowed competition or made gambling legal, people who like to gamble would have a higher chance of winning and there would be more money distributed to winners. So lottery-funded education is not free after all. Subsidizing education out of lottery proceeds punishes people who like to gamble. Those turn out on average to be people who are relatively poor with less education.
People like to defend the lottery by saying it's voluntary.
After all, you don't have to play. It's also true you can avoid the income tax by not working. So I guess that's voluntary, too. But it's hard to argue that the lottery is a voluntary tax when the government has a monopoly. Under a private, competitive lottery system, the prizes would be bigger and the odds of winning would be higher.