Thanks for the answers, they all make sense and upvoted all of them :)
So for a brief summary:
The action that I described in the question is far from optimal under EV framework (CarlShulman & Brian_Tomasik), and
Even it is optimal, a utilitarian may still have ethical reasons to reject it, if he or she:
endorses some kind of non-traditional utilitarianism, most notably SFE (TimothyChan); or
considers the uncertainty involved to be moral (instead of factual) uncertainty (Brian_Tomasik).
Thanks for the answers, they all make sense and upvoted all of them :)
So for a brief summary:
The action that I described in the question is far from optimal under EV framework (CarlShulman & Brian_Tomasik), and
Even it is optimal, a utilitarian may still have ethical reasons to reject it, if he or she:
endorses some kind of non-traditional utilitarianism, most notably SFE (TimothyChan); or
considers the uncertainty involved to be moral (instead of factual) uncertainty (Brian_Tomasik).