1. By showing that South Africa does not have a free market and is in fact a kind of collectivist welfare state for Whites only, Sowell argues that American conservatives have no valid ideological grounds to be in sympathy with the Pretoria regime.
(A) to be in sympathy with
(B) to sympathize with
(C) for sympathizing with
(D) that they should sympathize with
(E) that they should have sympathy for

Please tell me why the answer is C and not

'valid for' is the correct idiom. So ans is C