When it comes to unicorn blood, the books site the reason for its ghastly effects as a persons willingness to kill a creature as pure as a unicorn: but, what if you find an already dead unicorn? Would drinking its blood still have the same effects
I think unicorn blood must effect you negatively whether or not you personally kill the unicorn. Otherwise, there would probably be a black market in unicorn blood. Some wizards who are desperate or foolish enough to take the half life would kill the unicorns and sell their blood, and then rich wizards would buy and drink the blood and have all the effects of immortality without the negative consequences.