In lotteries, small to huge sums are given to random people who have done nothing to deserve that money and with regard to whom there is no special reason to assume they have the ability, judgment and intention to do anything useful or good with it. Therefore the value represented by the money is wasted and lotteries are undesirable.
There is more to be said about this, as illustrated by the following remarks commonly made to this point, and the responses to them:
Remark: The winners HAVE done something to deserve their prize; to wit: buying a lottery ticket.
Response: The act of buying a ticket is not an achievement so high that it needs to be rewarded; it is not a deed that creates or adds value. On top of that: Even IF one considers buying a ticket sufficient achievement, then EVERYONE who buys a ticket ought to be rewarded equally to be fair, and not just a few randomly chosen ones.
Remark: Given the small chances of winning, buying a ticket is a stupid thing to do, so those people deserve to lose their money and therefore lotteries are not per se unethical, but rather work as an "idiot tax".
Response: Although it is fair that ticket buyers lose money by being stupid enough to play in lotteries, the fact remains that the organizers of lotteries - whether state, private or charity - are making profit from an event that is bad for several other reasons explained in this article. And it must not be so that doing something bad pays off. The organizers do not deserve that profit. Unethical behaviour must not be or be allowed to be profitable. This response comes not out of "jealousy" or "spite", as makers of this remark sometimes say, but out of sense of justice, out of the deeply felt conviction of "Crime - or whatever unethical or undesirable act - must not pay".
And, there is another reason why unethical behaviour must not be allowed to be profitable: to prevent unethical people from acquiring large amounts of money which would enable them to infiltrate into mainstream business (by setting up formal enterprises around criminal or otherwise unethical activities), sports (e.g. by sponsoring), politics, and other aspects of society. Such interweaving of underworld and upper world is a serious problem.
Remark: Part of the profit of lotteries may go to charity, so that makes it good.
Response: If one really wanted to give to a good cause, it would be better to give the full turnover of an event, rather than to subtract prize money from it to be given to random people as described in the introduction. Then one would be giving more while avoiding the negative sides of lotteries. In addition, it is not generally agreed upon that charity is effective and therefore good. This is really a discussion in itself, but a fact is that there are many sensible people who observe that charity as practised in Western society, including developmental aid, is ineffective and similar to throwing money in a bottomless pit, and mainly serves as a trade in indulgences. If they are right, that in itself makes lotteries for charity pointless altogether.
Remark: The prize winners can spend the money they won, and the extra consumption thus generated by lotteries is good for economy.
Response: The notion that any increase in consumption is "good for economy" is mistaken, and originates in people who pull most of their income from interest, dividend and other ways of "making money with money", which (those ways of "making money with money") yield most in a growing economy and less or nothing in a stable or shrinking one. Therefore in the perverted perception of these capitalists, any growth of spending is good, even if the money being spent is not the consumers' own but borrowed, won or otherwise artificially pumped into the market. But in reality, the only consumption that is good for the market is that which stays within the buyer's budget. Spending more than one can afford always causes suffering in one way or another, and is only good for those who thrive on empty growth and are therefore fans of offering loans, systems for paying in installments, lotteries and any other way of artificially inflating consumption.