Just consider the heirarchy of life, different species, that you have in your head and how it isn't right. Appearance biases, largely. Valuing one more because it's fuzzier or cuter. People kill flies inside not because they're fearing disease. They do it because they can't be bothered to just let it outside. Way too many people will compulsively kill any insect they see, indoors or out. I assure you you'd feel better if you watched and appreciated it or ignored it instead of going straight to killing for no good reason. Worse still, killing in "funny" ways and recording/watching it. A kid kills ants with a magnifying glass, he gets sent to the counselor for a reason. "The world isn't a peaceful place" isn't a sound argument. And as the most intelligent species we're aware of, we should be above sadistic stuff for amusement.
If you want to continue, tell me what species would be the cut-off for blasting to death with a laser for fun. What would be the "highest"/"last" to be killed and what would be the "lowest"/"first" to be spared?