I've had this same conversation with religious scholars from all over the world. While we've discussed many biblical questions and issues, it's amazing that this one subject (what is or is not biblically considered reasonably as food) generates so much hostility. Maybe it's really true that a way that a man's heart is through his stomach. Or, maybe more accurately, a way to see what is in a man's heart is in his pantry.
There are really four New Testament passages that are used to defend abandoning a kosher diet. Most common is Acts chapter 10 when the sheet with all kinds of animals is offered to Peter in a dream (a dream that is talking about gentiles, not food). But, even so, God never suggests that Peter should eat "unclean" meat. He says, "What I have cleansed, call not common." Peter makes the distinction between "unclean" (animals not fit to eat) and common (kosher animals that have been in contact with unclean animals). God makes that same distinction, declaring that the common animals have been cleansed. People who use this passage to say that this Old Testament command is abrogated ignore this distinction.
In Mark 7:19, Jesus makes a statement, "thus declaring all meats clean." At least, in some translations he does. In any Bible translation published before the 20th Century, that phrase isn't there. But, even if it was, the Greek word translated "meat" is the word for food. Jesus was a Jewsh rabbi, speaking to a Jewish audience. "Unclean" meats simply were not classified as food.
In Romans 14:14, Paul declares that "nothing is unclean in and of itself." You have to go back to Acts 10 and see the distinction between "unclean" and "common" to understand this because the English translators don't make that distinction. The word that is translated "common" is the word used in Romans 14, not the word for unclean. The word for unclean is not found in this Text at all.
In Colossians 2:21, Paul uses an example of being forbidden: "(touch not, taste not, handle not)...." In context it is not suggesting that Jewish people be invited to touch and taste what the Bible has forbidden (note: the New Testament wasn't the New Testament yet). In fact, the notion goes completely against the very last words Paul is ever recorded saying in Acts 28:17, "I committed nothing against the people of customs of our fathers...." Instead, Colossians 2 may be understood as an invitation to gentiles that they should be able to participate in Jewish festivals (an idea that is consistent with all of Paul's teachings).
So, when these arguments are effectively answered, my opponent almost always responds with blind emotion: even to the point of rage.
First, I'm not telling anyone what they can't eat. I only explain why I choose not to. But, the manner of anger and defiance that results is uncanny. It always comes down to this: "I'm going to eat whatever I want to and nobody can tell me that I can't." And, I think therein demonstrates the uncleanness.
Jesus said, "It's not what goes into a man that defiles him. It is what comes out... For out of the heart of man proceeds evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies: these are what defile a man." (Matthew 15:17-19)
Maybe the whole food/not food issue isn't about food at all. Maybe there isn't really a profound medical issue that surrounds the avoidance of biblically unkosher. Maybe the whole thing is about whether or not we're willing to trust God above doing whatever we want.
Psalm 12 goes like this
Help, LORD; for the godly man ceaseth;
for the faithful fail from among the children of men.
They speak vanity every one with his neighbour:
with flattering lips and with a double heart do they speak.
The LORD shall cut off all flattering lips,
and the tongue that speaketh proud things:
Who have said, With our tongue will we prevail;
our lips are our own: who is lord over us?
For the oppression of the poor,
for the sighing of the needy,
now will I arise, saith the LORD;
I will set him in safety from him that puffeth at him.
The words of the LORD are pure words:
as silver tried in a furnace of earth,
purified seven times.
Thou shalt keep them, O LORD,
Thou shalt preserve them from this generation for ever.
The wicked walk on every side,
when the vilest men are exalted.