I have no cycling qualifications for commenting on this thread, other than to say fboab is much more tolerant of drinking from a bespattered bidon than me.
My view is - having mudguards would have ZERO bearing on whether I finish (a) at all, or (b) in time, from an aerodynamic POV, but might just save me from gastric distress that would prevent (b) and quite possibly (a) from a bacterial POV.
Sure - horses, cows and sheep are all vegetarians, but if the road is covered in their shit - it's still shit, and I don't want it on my water bottles thank you very much.