Blurring the distinction between 'methodological" and "ontological"

Habermas often makes a point that we should not try to read off ontological distinction of methodological distinction between the participant and the observer perspective. Habermas has often said that this confusion is the fountain spring of an idealist metaphysics. Robert Brandom attributes a similar position to Brandom in the following:

“Sellars . . . does not . . . subscribe to the Platonic principle that fundamental differences in kinds of being can be read off of structural differences in the ways we know them.” Overcoming a Dualism of Cocnepts and Causes, in TBGTM, 264.

Also see Methodological distinctions and ontological presuppositions