Why onions, garlic and leeks are seen as "non-vegetarian" foods(GDD-349, Master Sheng Yen)

Buddhism teaches that it's best to refrain from eating the five pungent spices. There are two reasons for this: when you're chanting sutras or when you're receiving guests, it is impolite and disrespectful if your breath smells bad. The other reason is that they arouse anger when eaten raw; when eaten raw before they're cooked, they make you irritable and ill-tempered. When eaten cooked, they arouse your passions; when you eat them cooked, they arouse your sexual desire and stimulate your sex drive.