"An absolute bar to the unity of Christendom": Keble on the dogma of the Immaculate Conception

In his A Memoir of the Rev. John Keble (1869), J.T. Coleridge quotes from a Keble letter of May 1855, referring to Pius IX's 1854 promulgation in Ineffabilis Deus of the Immaculate Conception.  Keble critiques the "distinctive" character of such Marian doctrines:

The Legendary services in the Breviary, with that for the 15th August at the head, are a standing instance of this; and so will this new doctrine be, in whatever degree they allege antiquity for it. They cannot but know in their hearts, that it has not the shadow of a Tradition ... Most fearful it is to me, that neither among the more moderate Romanists, nor among our Romanizers, (with one exception that E. B. P. told me of,) does it seem to have produced any sort of scruple or re-action.

Coleridge goes on to comment:

It will be seen how Keble speaks of the new dogma of the Immaculate Conception, and he felt the same as long as he lived. The promulgation of it pained him much; it constituted in his opinion, so long as it remained unrevoked, an absolute bar to the unity of Christendom. In this letter he specifies one objection to it on which in all such cases he relied much, that not only was there no authority for it in Holy Writ, but, as he expresses it, not a shadow of tradition. 

Keble's rejection of the dogma of the Immaculate Conception, together with his criticism of "our Romanizers", is a reminder of how Tractarianism - in contrast to much Ritualism and later Anglo-Catholicism - did not entirely lose the spirit and substance of the Old High Church tradition.