The closest we come to “society” “subsidizing” stock losses is via capital loss deductions. Assuming you aren’t doing particularly crazy tax shenanigans, you are looking at up to 3000 dollars deducted from your taxes per year. For reference, the standard deduction is 13850 for an individual as of 2023.
But the thing about capital gains and losses are that they are only actually a thing when you cash out of the stock market. This means you are actually encouraged to “sell” your shares in a failing company and use it to invest in a company “on the rise”. Which is actually good.
What you are proposing would, ironically, mean only the super rich would be able to trade stocks to begin with. And they would only invest in the “guaranteed” companies like MS and the like which would hurt a lot of medium sized companies and workers.
Also, this all forgets that the vast majority of retirement schemes (even pensions when you look at where the money comes from) are based on investing in stocks. In large part because the idea is to benefit from an overall better economy.
So yeah… your statement about “betting on black” makes no sense and your proposed solution only hurts all but the super-rich.