Chagigah 18: When Purification Requires Intent

A new mishnah: Washing hands prior to eating non-kodesh food, for ma'aserot, for terumot; and for kodesh (korbanot) or for a chatat, you need to dunk. But what if you've dunked for the purpose of eating regular food? You're presumed to be pure for the level of food that you dunked, but not for anything that requires a greater level of purity (whereas if you are pure for a higher level, you are considered pure for the lesser requirements as well). Also, a hierarchy is present for the potential impurity of one's garments. Plus, the experience of Yosi ben Yoezer and Yochanan ben Gudgedah. Also, do you really need to wash your hands if you're going to eat regular food?! And what about for ma'aser? It's all compared to a passage in Bikkurim. And opens the question what foods we wash our hands for and why.