The relevant factor isn’t income, it’s assets. It’s bad to have 20kUSD and no other investments, no matter what your income. On the other hand, in practice lower- or lower-middle class typically means having small or negative monetary assets. In that case, buying securities at all is probably a bad idea. First of all, there’s a research, setup and monitoring overhead to any such investment, and that overhead isn’t worth it if the amount you have to invest is too small. And second, the really high-return investments aren’t securities at all, they’re purchases of things that make your life better, save time, or help build marketable skills; and the less money you have the less likely it is that you’ve hit diminishing returns on those sorts of investments.
The relevant factor isn’t income, it’s assets. It’s bad to have 20kUSD and no other investments, no matter what your income. On the other hand, in practice lower- or lower-middle class typically means having small or negative monetary assets. In that case, buying securities at all is probably a bad idea. First of all, there’s a research, setup and monitoring overhead to any such investment, and that overhead isn’t worth it if the amount you have to invest is too small. And second, the really high-return investments aren’t securities at all, they’re purchases of things that make your life better, save time, or help build marketable skills; and the less money you have the less likely it is that you’ve hit diminishing returns on those sorts of investments.