"Stupidity" (innumeracy, really) is a prerequisite for finding the lottery entertaining. The thought of "what if" is predicated on the idea that buying a lottery ticket meaningfully increases your chances of winning. You may as well fantasize about finding a bag of money in the street; it's cheaper and the expected returns are better. And as for "money you can afford to lose" - there's no threshold where money stops being money. Buying one lottery ticket is just as fallacious as buying a thousand; the only difference is the magnitude of the error.

On the other hand, if you do find the lottery entertaining - despite how irrational it is to do so - no amount of lecturing or calling you innumerate will change your mind. So you may as well buy the damn lottery ticket :)