This is a good argument against lotteries but not as good an argument against sports gambling. If you are better at sports prediction than the bookmakers, you can make money. Nobody gambles as an "average person", they gamble as themselves, and convincing an individual that they personally are bad at predicting outcomes requires more than saying "most people can't do it".
People see it as a game of skill where they win money from people who are worse at that skill than they are.