Full Idea
The superfluous transcendental 'I' is actually a hindrance. If it existed, it would violently separate consciousness from itself, it would divide it, slicing through consciousness like an opaque blade.
Gist of Idea
If the 'I' is transcendental, it unnecessarily splits consciousness in two
Source
Jean-Paul Sartre (Transcendence of the Ego [1937], I (A))
Book Reference
Sartre,Jean-Paul: 'The Transcendence of the Ego' [Routledge 2004], p.7
A Reaction
I see no a priori reason why consciousness should not be split in two, if that's how it is. Personally I am happy with a fairly traditional Cartesian view, that the self is the will and understanding, and the rest of consciousness is its working material.