I call it "manga," because the term usually makes a useful distinction between comics of the western style, and those of the eastern. Japanese comics as a whole are distinctive enough that, purely from a linguistic standpoint, the additional information provided by the word "manga" is worth using it, so to speak.
Of course, "manga" is just a translation of "comics". That hasn't stopped it from becoming a specific term in its own right. Language changes over time to fit the uses that people need from it, is all.