The probability in my mind that I am correct in attributing extensive moral personhood to other humans is very high. With non-human vertebrate, I attribute slightly less extensive but still quite broad moral personhood, and I am in this too quite confident. But I accept given I am a fallible human being I might be wrong and should give them no moral personhood or moral personhood of the kind I ascribe to humans.
Continuing in the same line, I ascribe almost no moral personhood to bacteria and viruses. But again given I am fallible musnt I accept some non-zero probability that they deserve human like personhood? If so, and I am a utilitarian, given the extremely large number of bacteria and viruses on the planet it seems even if I am very sure that bacteria are of only minimal moral importance, I still must make serious concessions to them because it seems doubtful that my certainty is so high as to overcome the vast numbers of bacteria and viruses on this planet. (I am aware it is not entirely clear how best I could promote bacterial welfare but even so, it seems I simply cannot be as certain as I would want to be to disregard them as much as I would like). Am I missing something? Is there a solution to this problem?