With all due respect, do not be lazy about your quotes..  Give page numbers as well as book titles, context is very important...  Not saying you are doing this, but quotes without context or edited can be easily twisted one way or another... At least by giving the page number, oh and saying it is hard back or paperback as well because the pages don't always line up, gives the rest of us to go back and read for ourselves...  It enhances the debate and give both sides of it better grounds to support or refute..

The council say that killing non humankind does not violate the 7 laws, whether or not it cause taint however is another matter entirely.
 
Harry use forzare to kill the fetch in book 8, and he get lost in battle lust. The fetch is non human, but it is shown to us in book 9 that Harry's control of his temper is growing steadily worse by the day.
 
It is entirely possible that unjustly killing a supernatural being, say killing a bigfoot like river shoulders, will cause some kind of taint even though the council won't acknowledge the act as a law violation. It seldom happens though. When it comes to supernaturals and wizards. The ones who has good intentions won't come, and those who come don't have good intentions. The way things are going, it is well nai impossible to unjustly kill a supernatural.