Gambling has always been a tax for the mathematically illiterate. Casino gambling has always been a scam and this proves it--whenever someone too clever comes along, they run right to the muscle to get their money back.
Even if you 100% know the odds are nowhere near your favor its possible to get pleasure from the act of putting down a bet, even if you lose. It can be a form of entertainment.
I, personally, don't get this pleasure but I can understand other people like different things than me.
Whether or not it should be legal, its additive potential is too much of a burden on society, or is ethical is a different question entirely.