Please enumerate the reasons why it would be wrong to kill Duncan in Macbeth's opening soliloquy of Shakespeare's Macbeth.

Although I disagree that this is Macbeth's "opening
soliloquy," I know the precise moment to which you are referring:  Act 1, Scene 7. 
(It's one of my favorite pieces of evidence, actually, that it's Lady Macbeth and not
Macbeth himself that is the true evil force behind this foul murder.)  In short, Macbeth
gives four precise reasons for not wanting to kill Duncan, ... or "why it would be
wrong" as you say.

First, Macbeth is afraid of eternal
fire.  Macbeth says that "We'd jump the life to come" and they would "plague the
inventor."  Well, yes, I would say.  No one ever wants to "plague the inventor"!  Murder
is certainly a most foul way to do it, too!  It's interesting, in my opinion, that this
is the first reason Macbeth gives.  It would certainly be enough for me to stop dead in
my tracks!

Second, Macbeth is afraid of being killed
himself when he does become king.  (How ironic!)  Look at this
line:

This
even-handed justice / Commends th' ingredients of our poisoned chalice / To our own
lips.

Macbeth, then, fears
drinking from this same "poisoned chalice."  It's just a fancy way of saying that fate
will, most likely, come around.  Death will be waiting for Macbeth if he does this, king
or not.

Third, Macbeth will be nixing something very
important:  loyalty.

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He's here in double trust: / First, as I am his
kinsman and his subject, / Strong  both against the deed; then , as his host, / Who
should against his murderer shut the door, / Not bear the knife
myself.

Macbeth speaks of
Duncan here.  Duncan is trusting Macbeth in two very important ways.  First, as
kinsman/subject, Macbeth should always serve the king by protecting him.  Secondly, as
host, Macbeth should do the same.

Fourth, Duncan is a good
king; therefore, he shouldn't be killed.

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Besides, this Duncan / Hath borne his faculties
so meek, hath been / So clear in his great office, / that his virtues / Will plead like
angels trumpet-tongued against/ The deep damnation of his
taking-off.

It's pretty
amazing, actually, how Macbeth enumerates the reasons why Duncan is a good king.  He's
humble, "clear in office," and virtuous.  By the end of this soliloquy, one wonders why
Macbeth is even listening to his foul wife!  I'll admit, too, that each time I read it,
I root for Macbeth to reveal the plot to Duncan and divorce his wife.  I'm afraid I'm
always disappointed.