I'm a newbie, at only two years and change.
Was it cruel? Maybe. Was it the cruelest thing in Trek? Probably not. I can think of several worse things that Trek writers had happen to characters. Kasidy losing Sisko, Carey dying just weeks from Voyager getting home, Trip and T'Pol losing their baby right after meeting her, Lwaxana losing a child and then feeling that she has to erase her from her life, O'Brien getting essentially tortured for twenty years (even if it didn't happen), a whole planet dying while Picard spews some lame-

speech about "honoring the lives we cannot save"... I could go on and on.