@Cori6 The short answer is, in my opinion you should write a tactful thumbs-down review, indicating that the bedroom and bathroom were left in a very unsanitary state but leaving out the embarassing details. This may make it difficult for them to get another Airbnb booking, but that's not a bad thing - there's no host out there who wants to deal with fecal matter, no matter how nice the guests are otherwise.
The long answer - well, if you ask any hotel housekeeper you'll hear horror stories like this and worse every day. (In fact, the more you know about hotels, the less likely you'll ever want to stay in one again). Unlike Airbnb hosts, hotels use heavy-dury industrial laundry services, and the rooms are designed to be more easily disinfected than a typical household. The invisibility of maid service (and all the class/gender dynamics that come with it) have conditioned hotel guests to treat their rooms with no concern for the person who has to thanklessly clean them. The closer our listings come to taking a bite out of the conventional hotel market, the likelier we are to get guests like that.
Is it to be considered acceptable? I would say no. Guests are staying in my home, and I expect them to treat it at least as well as they would want their own home to be treated - which at a bare minimum would mean not leaving poo laying around. The higher prices hotels charge include daily housekeeping service, and those who forgo that for the lower price I offer have to accept a bit more responsibility for the state of the household. I did have an elderly guest once who became very ill and suffered incontinence issues during his stay, but he was also considerate enough to clean up after himself and leave the bathroom and bedroom in an agreeable state. So I certainly see no need for hesitation in hosting senior citizens or people with medical issues, but I do pay attention to how respectful and considerate the guest's initial communication is.
For our part, we should be sure to communicate in our listings what condition we expect the property to be left in; this is especially true for offsite hosts like you. "No poop in the bed" is a given, but it's not obvious to all guests that they're expected to wash their glasses or clean the bathroom, for example. Another suggestion I can offer is that you consider increasing your minimum stay to at least 2 nights; many hosts find that the one-night-only guests make the worst messes since they don't have to wallow in their filth for another day.