I don't get the impression that many of us prefer people to remove shoes because of any fear of germs - very few, in fact. Most of us do it because of the general dirt that is trailed in on wet shoes.
Doormat have been mentioned, but I have one outside the back door then a large one inside it, yet I can still clearly see dirty footprints on the kitchen floor where people have walked in their shoes after supposedly using those mats.
I don't mind that, as it can be mopped after they have gone, but it is quite clear from the carpet in the living room that their shoes were still not clean or dry by the time they stepped from kitchen to living room.
I can't afford a carpet shampooer or a steam cleaner, and wouldn't even have anywhere to store them if I did, and getting down on my hands and knees to clean grime from the carpet with special shampoo hasn't kept it clean.
We live in a small house, so perhaps the problem is greater than it would be in a larger house where a similar amount of dirt would be spread more thinly over a larger area.
Also, parking is either on the road or the (frequently-muddy) grass verge at the end of our long front path, so visitors will always have soiled shoes by the time they reach our door in winter, and quite often in summer too, though they probably aren't aware of it if they left home in clean shoes.
I don't think it's at all unreasonable or overly-houseproud to want to prevent carpets from becoming (and looking) grubby within a few months of being fitted!
If you are lucky enough to live in a house where this doesn't seem to happen for whatever reason, or if you simply don't care, that's fine too. I certainly don't mind keeping my shoes on if that's what the person I am visiting would prefer. Their house, their rules 