I state very clearly that as a host I will occasionally have to enter the PRIVATE guest room and bath when the guest is out - multiple times in the description and house rules.
I also state in my description that I do not touch or disturb the guest's personal items and I have a safe in the room that the guest can use to store any valuables or cash.
The reason I enter the guest room is more or less same as @Ken28 - in that I like to keep an eye on the place, maybe ever 3~4 days? I do trust my guests - I let them into my home, and share my space with them! It does not mean I should not and cannot enter the guest room which is a part of the home I own!
Every couple days I also do a quick vaccum of the floors and under the bed, and like to air the room so it doesn't get too stuffy while the guest is out. (My place is a new construction so the smell of new furniture and paint still lingers if the door and window is kept closed all day) I also either make the bed and check to see if bedding needs to be changed.
I collect used towels and also check if the guest has run out of kleenex, TP, and empty the trash. Also in Seoul we have serious air polution problems with yesllow dust. If the window is open on days when the air quality is bad, the room will be covered with layer of yellow dust within a couple hours - just as bad as an open window during a rain storm!!!
Hotels have housekeeping. If the listing is a private room where the host also resides and there are shared common areas, and if the host has made it clear that they may have to occationally enter the room and explain the purpose of entering the room when the guest is out, I honestly don't see why this would be a problem.
I once found a bag with what used to be a couple oranges covered in fungus with some of the spores escaping the bag and getting on the floor and furniture when I entered my guest room to vaccum once. I took a picture and sent my guest a message that I would be cleaning this up and disinfecting the room and changing all.the bedding to make sure all the fungus spores are gone. My guest thanked me for cleaning it up and appologized that she totally forgot the oranges were there.
If any potential guest is not comfortable with me entering the room to do some basic housekeeping, then that means they are not a good fit with my hosting style, and should have read my description carefully instead of complaining about something that is clearly stated. I have a long description and make it very very clear to the guest what they can expect if they reserve a room with me.
I honestly don't think Airbnb has the right to dictate whether hosts should be allowed to enter guest rooms or not. It is up to the host to determine their hosting style - and if hosts are honest and clear about these conditions to guests, Airbnb does not have the right to say otherwise!