As a small investor, borrowing money to invest is almost invariably a terrible, terrible idea, because any return you make on the investment will likely be cancelled out by the interest paid to borrow the money.

I just looked up margin interest rates, for loans of 10 000 or less (which is what we are likely talking about with robin hood) the interest rate is Base Rate + 1.25% which is 8.50% interest. I don't know many stocks you can buy even in the best of circumstances that will get you a guaranteed return of more than 8.5%. Moral of the story - robin hoods retail investors should not engage in margin trading.