No of course not. But that's not the question. The question is, suppose you've got a lump sum. Would you rather take a risk free 4.x% return by paying off your house, or take on some level of risk -- still far from high risk -- to earn quite a bit more than that.
The OP made the "risk-free 4%" one of his top must-do's. My point is, that's not always the case. Paying off debt is not always the best choice in the current times of very cheap borrowing.
YOU have no appetite for risk (judging only by this comment). That's not true of everybody.
In other words, show me a zero risk 5% vehicle and I'll stop trying to pay off my mortgage immediately.
edited for a dumb mistake....