Aristotle also believes that lack of self-restraint in regards to "spiritedness" (i.e. when our "blood's up") isn't quite so bad as it is with other passions.
This is because there is some sort of reasoning involved in outbursts, even though the reasoning is distorted.
People also have sympathy for those who get carried away, since it's natural. Also, spiritedness doesn't act in a pre-meditated way—it's impulsive, a reaction—which is more forgivable.
It's less deceitful than desire, which Aristotle describes as general lack of self-restraint (kind of like vice with a capital "V").
To put the nail in this coffin, Aristotle brings in hubris. A spirited person acts out of pain, not out of conceited notions of their worth. A person driven by pleasure is "hubristic."
Aristotle says that brutishness is "lesser than vice, but more frightening." This is because a brutish person has a destroyed soul. Dang.
He says that any person who's the origin of his own baseness is worse than those who aren't (i.e. voluntary wickedness v. involuntary wickedness).
So an unethical person is infinitely more harmful than a brute animal.