Getting both sides of this arg: basically 'sep of concerns' is viewed as being 'seperation of technology' rather than actual sep of concerns. Eg, put documents and styles and behaviour for a related component together, seperate that component from other components.
It's a slightly silly argument because really we're arging between slicing something vertically (tech) vs horizontally (components) and the nicer thing is probably to do both - have lots of components with the documents, styles, and behaviour separated out within each component.
1) Semantic markup for the sake of screen readers (and Google and so on)
2) Separation of concerns for the sake of maintainability
I don't know how separation of concerns cause grief for developers, my experience is the opposite. Separation of concerns not a "fad", it is a fundamental principle of any kind of systems design. That said, it doesn't directly affect users, just as users don't care if you write incomprehensible spaghetti code.