The dangers of city life concern the narrator of Howards End greatly, but they're not necessarily the fears of the big, bad city that we might expect – there's nothing dramatic about violent crime or inner city corruption. Rather, the novel is concerned with the less flashy, but no less alarming dangers of living in London: the damage it can do to one's character and personal relationships. The narrator and some of our characters are agitated by the continual flux of the city, in which things are constantly coming and going. London is portrayed like a kind of beast that consumes everything that crosses its path, from individual people to whole villages, and the threat of urban and suburban sprawl haunts the whole novel.
The country, on the other hand, is depicted as a space of real, proper Englishness – a place where the characters can truly connect with the land that they all come from. There's something real about the countryside (whether in Oniton or Hilton) that gets to both Margaret and the narrator – and, through them, to us, the readers. Country life seems to be somehow more substantial, natural, and, well, human than city life, and the relationships that people have both to each other and to the land itself seem more valuable there.