Leviticus revisited

Before the Christian scholars gang up on me, I'll confess that, yes, I know a key passage in The Acts of the Apostles (Peter's dream) did away with the Law's dietary restrictions for Christians:

11:1 And the apostles and brethren that were in Judaea heard that the Gentiles had also received the word of God.
2. And when Peter was come up to Jerusalem, they that were of the circumcision contended with him,
3. Saying, Thou wentest in to men uncircumcised, and didst eat with them.
4. But Peter rehearsed the matter from the beginning, and expounded it by order unto them, saying,
5. I was in the city of Joppa praying: and in a trance I saw a vision, A certain vessel descend, as it had been a great sheet, let down from heaven by four corners; and it came even to me:
6. Upon the which when I had fastened mine eyes, I considered, and saw fourfooted beasts of the earth, and wild beasts, and creeping things, and fowls of the air.
7. And I heard a voice saying unto me, Arise, Peter; slay and eat.
8. But I said, Not so, Lord: for nothing common or unclean hath at any time entered into my mouth.
9. But the voice answered me again from heaven, What God hath cleansed, that call not thou common.

I am also aware that in The Epistle to the Romans, Paul goes to great lengths to argue that the Cross supersedes the Law:

3:20. Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
21. But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
22. Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
23. For all have sinned, and come short of the glory of God;
24. Being justified freely by his grace through the redemption that is in Christ Jesus:
25. Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God;
26. To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.
27. Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith.
28. Therefore we conclude that a man is justified by faith without the deeds of the law.

I continue to cite Leviticus 11 only because the anti-gay, literalist Christians continue to cite Leviticus 18:22

Thou shalt not lie with mankind, as with womankind: it is abomination.

Why has this single verse been exempted from Paul's amnesty?

How are we to interpret the Bible as the literal, eternal, inerrant Word of God if these exceptions be so arbitrary? Which of G-d's laws ought be made the basis of the Constitution?