PyroManiacs ask some good questions in their post: Nineteen questions for signers of "The Manhattan Declaration.” The issues the declaration addressed were important but not more important than the Gospel it downplayed to allow for unity of the signers. While I think that many of the signers were well meaning I think the message given with regards to the Gospel is that some issue are just too important.
Also here are some comments from James White on the declaration:
The Troubling Aspects of the Manhattan Declaration
Further Thoughts on the Manhattan Declaration and a Response to Frank Beckwith
And from John MacArthur: The Manhattan Declaration
From Steve Camp: The New Downgrade….12 dangers of Evangelical Co-belligerence related to The Manhattan Declaration.
Also here is Al Mohler’s reasons for signing the declaration: Why I signed the Manhattan Declaration