For me, the choice in all cases is clear: it's pretty much always a bad idea to borrow money and invest it in the stock market - and it's an even worse idea to borrow money against your house and invest it in the stock market. Because that way you not only risk losing money in the market, you also risk losing your house. I'm sure you can come up with an extreme example of "well-heeled and well-capitalized folks" for whom your idea might make sense, but even there I'm having difficulty working out why people who are so well-heeled (and who therefore have diminishing marginal utility of future returns) would feel the need to leverage their investments in such a manner.