Hey Tynan, love your blog posts usually but this seems really irresponsible!
1. There's no such thing as "no risk". What happens if your real estate friend ends up losing all the money because the market suddenly turns bad? (not saying your friend doesn't know what he's doing, but all investments have risks)
2. There's a difference between a banking and a brokerage account. For example, in UK, money deposited in a bank is generally protected by the FSCS, which means you get (a lot of) your money back if the bank goes under. Brokerage accounts don't always have the same protections.
3. If Interactive Brokers go under, you no longer have a margin account. You only have to look as far back as 2007/2008 for examples of this kind of thing happening! Even if you can get your money back, it'll be months later... It's important to always keep some emergency cash around.