Let me state here and now that I have not read all the posts here as it is currently *WAY past the time I should have gone to bed...
But I am a Christian, and I follow Leviticus 11/Deuteronomy 14. I have thought of and heard the reasons mentioned, and also I have heard that the unclean animals were the trash eaters, natures' disposers.
As for Acts 10, read the following verse, and it is explained the verses are not contradicting the OT.
As for Matthew 5:17-21
The Fulfillment of the Law
17"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. 19Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven. 20For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven.
Im not sure how well, if at all, Mike addressed this, but I will give it a shot.
Jesus said He came to fulfill the law. He came to make it complete. Thus, He did not cancel the OT law, but finish it. The law still applies, but we now have a course of action when we break it. Yes, Jesus' death removed the need to offer animal sacrifice, because He is the perfect and ulitamte sacrifice. However, the rest of the OT, if it is not like animal sacrifices (fulfilled) still apply. What Matthew 15:11 states is really rather simple. What you eat isnt what makes you clean or unlcean, but (adding a few verses togther) what is in your heart. Remember, what uttereth from the mouth reveals the heart, and the verse says that what utterth from the mouth is what makes a man clean or unclean.
I could go in to a long winded and detailed explanation on what the OT law was and what Jesus' death did to it (in boiled down terms) but I shall save you from it and turn to bed....