To be able to properly answer this question about the poem "The Rime of the Ancient Mariner," it is important to be able to read the full quote by Samuel Taylor Coleridge in its specific context. "The Rime of the Ancient Mariner" was first published in 1798 in the collection Lyrical Ballads. This quote appeared in a book called Specimens of the Table Talk of Samuel Taylor Coleridge, and the date given for this talk is May 31, 1830. Here is the full quote:
Mrs. Barbauld once told me that she admired the Ancient Mariner very much, but that there were two faults in it,-it was improbable, and had no moral. As for the probability, I owned that that might admit some question; but as to the want of a moral, I told her that in my judgment the poem had too much; and that the only, or chief fault, if I might say so, was the obtrusion of the moral sentiment so openly on the reader as a principle or cause of action in a work of such pure imagination.
Coleridge goes on to explain in the talk that the Ancient Mariner poem should have had no more moral than a tale from the Arabian Nights in which random magical events occur for no apparent reason. The tale he refers to has to do with a merchant who stops by the side of a well. While eating lunch he tosses date shells aside. A terrible genie with a scimitar appears and tells him that the merchant had accidently killed his son with one of the shells, so now he must die. In giving this example and in saying that "Ancient Mariner" was too moral, Coleridge is saying that because the poem is such pure fantasy, the moral should not have been so obvious.
In answer to your question, whether you agree with Coleridge's viewpoint that "The Rime of the Ancient Mariner" is too moral and the fantastic events should have been more random and morally ambiguous is a matter of personal opinion. You should decide this for yourself. In formulating your opinion, though, you might want to keep in mind one of the most moralistic stanzas, which appears near the end of the poem.
He prayeth best, who loveth best
All things both great and small;
For the dear God who loveth us,
He made and loveth all.
The mariner kills an innocent albatross and as a result has to suffer many torments. He learns in the end to love and respect all of God's creatures. This is one of the main morals of the poem. Is it appropriate for Coleridge to express this so obviously? Should he have been more subtle? Or should he have left out the moral completely?