By that measure, isn't working putting your time at risk? After all, the company could collapse and go under any day, or, more likely, just lay you off any day!

(I realize that equity instruments are far riskier than working, but debt instruments really aren't. With a bond or loan, the company owes you the money either way, just as it does when working for salary.)

I see no reason that realized capital gains shouldn't just be treated as Yet Another Source of Income.