Robinson also killed three of the JLI during his Starman run, including Crimson Fox, Blue Devil and a Amazing Man who, just a few years prior had been holding their own as interesting characters in their own title. The fan reaction was also bad as they were killed in the space of two or three pages and rather ignobly.
And then, as now, he did it to pump a lackluster villain, to show dangerous that villain is. In that case, the "new" Mist, Nash...who he killed at the end of his arc a few issues later.