Doctor LeBon was interested in taking the resources from this planet, and bringing them to Earth, as he had planned on cutting the world in half by using his Planet-Splitter, although he was unaware that the machine didn't work.
As far as it was implied, the world was uninhabited, and therefore no forms of life, or at least intelligent life existed on this planet. It is possible that some form of life did exist however, in fact Marvin White indicated that Superman wouldn't like it if LeBon destroyed a planet, as his very own homeworld of Krypton was also destroyed, which killed billions of people.
It's uncertain if there was billions of people on Cygnus-Uno, but if there was, that would have definitely made the incident a very controversial one, since LeBon would have apparently been murdering billions of alien lives just to extend the life of the human race. It's unknown whether or not LeBon had known if life was on or not on the planet, but if he did know that there certainly was, then that speaks volumes of his personality, showing that he's willing to kill many to save many, which could be considered evil in its' own right.