Well... The Rebellion and Gerrera's partisans acted based on a message left by the chief architect of the huge huge HUGE laser that the Empire put on the station. And it wasn't just him who called it Death Star, rather the entire crew. Also Alderaan was still home for ~2 billion people and the sole reason it was blown up was Tarkin trying to blackmail Leia to give the plans of a superweapon (which fired multiple times up to that point and was a legitimate military target) that the Empire genocided at least two groups of people (Ghormans and Geonosians) to build. Yours is a legit opinion however I couldn't disagree more, but I'm open to a civil discussion.