I'm all for debt if used responsibly. Getting a mortgage can - depending on your personal financial situation and the market conditions - be a good decision. But paying it off versus buying a bunch of gadgets or a new car should be a no-brainer. Unless you have a guaranteed ROI on some investment plan.

It doesn't need to be guaranteed, it just needs to be better expected value, with a volatility you're willing to accept.

Risk, like debt, is not always a bad thing, as long as you're informed and understanding of it.

As Daniel Kahneman said in 'Thinking, Fast and Slow', people ought to take more opportunities with risky outcomes with positive expected values - some you will lose, but over your life, taking a large number of these risks will result in a positive outcome.

(Obviously, only take risks where the negative outcome is one you can get through, i.e. it won't kill you, or leave you completely penniless etc.)

In any kind of gambling, including investing, variance is the killer. Unless you're making extremely small bets compared to your total bankroll, the inevitable down-swing will end you. The "take risky opportunities" advice is only valid if you can afford the worst possible outcome and still keep going.