The same justification as when you place a bet on black in vegas, it comes up red, and the house takes all the chips you bet.
You can call greed “rational self-interest” and gambling “speculative investment” all you like, but trying to change the language doesn’t change the reality.
When you’re gambling, you might lose, and society shouldn’t subsidize the days you gamble and lose. Only income derived through labor should be truly safe, as labor is useful to civilization, unlike gambling, often with winnings from previous gambling gained using loaded market influence dice and marked insider information cards.