That's true, but given that bankruptcy laws provide an effective floor for how badly you can suffer due to losses, and getting rich can provide for superlinear utility of money for some people (especially since being a savvy investor is very high status), I would expect that some would find the shut-up-and-multiply outcome positive given their preferences. This especially in the context of MWI, in which this strategy guarantees a roughly predictable future mix of your impoverished (but not horribly suffering), reasonably well-off, and super-rich and high-status future selves.

Of course, I don't think that this is implied by MWI as such; that's why I wrote "some of the MWI proponents."