You know, I think I might have said the same when I was millennial-aged (though I know that financial life was easier back then: easier to get on the property ladder, lower student debt). I didn’t have a margin account but I did invest all of my waking hours, a relationship and all the money I had into a startup, which as an investment mostly failed.
But the prospect of a margin account terrifies me now. I think they are dangerous.
The thing that 40-something me would say to millennial me is that you don’t need the leverage and risk of investing in startups or getting a margin account because you already have leverage: time. If you’re about 20, you have around 50 years of investing time. In that time you could easily get rich slowly, and with minimal risk compared to margin accounts.
(For another good example of investing in things with higher volatility and uncertain risk/reward, in that post I linked to immediately above, I said that Ethereum was a +50% winner for me. Now it is a -37% loser. That’s in 2.5 months.)