Drew,
I'm not sure that the Levitical food laws were in place because they "defiled" a man.
My thoughts are a little scattered here, so hopefully I can be somewhat coherent with this thought, please bear with me.
To start with, Adam and Eve's food was very easy: They and the animals had free range all all food bearing plants except the fruit of the Tree of Knowledge. That was the first food law, that they weren't to eat from that tree. We all know that they disobeyed. Even after they broke that law and were defiled, the issue of food remained the same until after Noah. Basically, everybody was a vegetarian.
The next food law is found in Genesis 9:3-4: "Every moving thing that is alive shall be food for you; I give all to you, as I gave the green plant. Only you shall not eat flesh with its life, that is, its blood."
Here, all the animals, not "clean" but all the animals could be eaten, but again God put a condition: not to eat the blood.
As far as I know, that is the only food prohibition until we get Passover, where the meal was carefully dictated, an unblemished lamb, roasted in fire with bitter herbs, unleavened bread, etc.
Then, when we get to the Levitical food laws, there are all kinds of prohibitions in place, some of them make a lot of sense, some of them seem very arbitrary. I can understand the dietary dangers of pork among a people who were on the move and proper curing was impossible, but come on, what's wrong with shrimp?
Keep in mind also that it wasn't just that they couldn't eat the forbidden foods, they couldn't even touch the carcass.
This all makes it seem to me that it was never about the specific food.
I'm going to post the text here, just to make it easy for me:
Mark 7:14-23 (New American Standard Bible)
14After He called the crowd to Him again, He began saying to them, "Listen to Me, all of you, and understand: 15there is nothing outside the man which can defile him if it goes into him; but the things which proceed out of the man are what defile the man. 16["If anyone has ears to hear, let him hear."]
17When he had left the crowd and entered the house, His disciples questioned Him about the parable.
18And He said to them, "Are you so lacking in understanding also? Do you not understand that whatever goes into the man from outside cannot defile him, 19because it does not go into his heart, but into his stomach, and is eliminated?" (Thus He declared all foods clean.)
20And He was saying, "That which proceeds out of the man, that is what defiles the man. 21"For from within, out of the heart of men, proceed the evil thoughts, fornications, thefts, murders, adulteries, 22deeds of coveting and wickedness, as well as deceit, sensuality, envy, slander, pride and foolishness.
23"All these evil things proceed from within and defile the man."
I guess what I'm getting at is that the "unclean" foods were forbidden, but not because they defiled the man. Rather, those who would eat those forbidden foods, showed disobedience to God, just as Adam and Eve did. Their disobedience proceeded out of their heart. That was the defilement of the "unclean" foods.
As I think you mentioned earlier, the Law was a tutor, a harsh taskmaster meant to bend the will to God. But, its purpose was always to point out how impossible it is for us to obey God. The law called upon us to obey God regarding not eating shrimp and suddenly we get an overwhelming for some scampi. That was the whole point of the law, to expose our disobedient nature.
So, I guess what I am getting at is that Jesus wasn't contradicting the Law by saying that nothing one eats defiles him, but rather pointing out that the food itself wasn't the defilement, but rather our disobedient nature regarding God that was defilement.
I hope that made some sense.