if people misuse of a specific term in a casual context made the term meaningless, we wouldn't be able to speak of politics, science or any other specific field. Alt-right has a very specific meaning in politics and political analysis, regardless of how it's used in a casual context
"Alt-right" isn't any sort of established term of art; it was first coined in a casual context less than a decade ago. I've seen some researchers use it as a kind of synonym for "white identity politics", but it seems to me that they're doing so specifically because of the casual usage, not because the term is particularly useful to them.
