Well I wouldnt say shoot the first thing that walks out. You dont want to kill something too young that might grow up into a decent buck if you let it go another season or a tiny little doe. Definatley make sure its worth shooting, but dont be picky in terms of not shooting at anything unless its a Bambi's dad.
"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling which thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
-John Stewart Mill