Don't get me wrong, while I did like DBZ in the past what I always hated was it's lack of consistency. The arc when Vegeta was coming towards earth him and Nappa encountered a peaceful planet which Vegeta with minimal effort pointed, laughed, and destroyed...yet look at how long and how much effort he used and only things like a mountain gets destroyed. I also agree with you, if your home, friends, family, community... iow the whole thing was going to be destroyed why fight fair?
@John_Doe_Jersey Dragon Ball has always been rather bad at showcasing the ridiculous impact this sort of powers would have on the environment. The destruction stays at the same level even though the power levels have been multiplied by a few quadrillion times.
Most fan works just wave it off as people learning to nullify the excess leaking energy from their punches that doesn't get transferred to the opponent and creating more concentrated Ki blasts that just annihilate everything caught inside without destroying everything with the force of a trillion suns. The real answer though is that Toriyama just wanted to make a fun martial arts manga and didn't think things through and excluded the environment outside of narrative reasons from the fights.