I hadn't really thought about it, like many here have already stated, I'm pretty barefoot most of the summer usually wearing some sort of slider and as the name suggests often slide out of them altogether, probably not at someone's else's house maybe. Having said that some people's feet aren't terribly attractive, but I guess like other parts of the body that's all in the eyes of the beholders!
I often had the dilemma when we lived in our previous house, we had a living room on the first floor, when my kids were in their teens they'd tell their friends to take their trainers off in the downstairs hall, it was very much a case of what was the least offensive, the smell of odorous un clad boy feet or a bit of mud on the stair carpet, often the latter seemed the best option 