In a war between Earth and Venus, the Venusians discover records of a horrible weapon which in their desperation they turn on humans.

This is a bad story, nearly as bad as "Half-Breed". It shares the pulp sf view of the solar system (bad astronomy, bad, bad), it has a primitive style with thin, cardboard characters. And, as Fred Pohl observed, the instant after the Venusians destroy the weapon at the end of the story, the Earthmen surely would attack them again at once and wipe them out—and "The Weapon Too Dreadful to Use" does, in fact, get used, so the plot is silly and the title doesn’t make sense, not to mention being way too melodramatic. (Pohl’s second remark helped sour Asimov on long titles.)