The dog brings in more muck than a pair of clean shoes
I was finding this thread extremely amusing, without exactly being able to analyse why, until I came to the comment above and reflected on my four cats and their open 24 hours a day cat flap. Cats are, of course, very clean animals but they are very clean because they constantly wash and as they wash they carefully deposit on your chairs, bed, etc all the surplus fur, seeds. bits of grass and pollen and blossom and general muck they've just removed from their coats. A friend commented that she'd never met anyone who did as much washing as I did and I explained it was because every chair, bed, etc, (even the printer which they regard as a comfortable place to lie) has a throw or towel over it and these constantly need to be washed. Needless to say hard flooring throughout in my place.
I'm happy to keep my sandals on - I don't wear socks or tights - or take them off in other people's houses as they personally wish but I expect a direct request not to have to guess at what they want. The fact that a householder is wearing slippers doesn't inform me that they never wear shoes in the house, rather it tells me that they've been in for a period of time, plus, of course, I've come across many people who wear slippers in their house for comfort but don't stop to put on shoes if they want to walk round the garden or down the garden path or go to and from their car to fetch something. Also a pile of shoes beside the door means nothing as some families use that place as a storage area for all their footwear and it tells you nothing about their habits and wishes as regards shoe wearing in the house by themselves or anyone else.
People in my house? I don't care, they can take their shoes off or leave them on. I do prefer however that they don't sit down and start licking their feet - only cats can do that with real elegance.