I agree that sometimes they will only take live, but I feel some people jump to live to solve their non-feeding problems (with adult snakes that is) too quickly than really needed anyway.
And I think there are exceptions of course. Its when people say "oh its so cool" and "Its nature" without realizing the terrible logic mistake they are making in saying that. IMHO nothing is natural about a snake feeding in a small enclosed area with no escape hole/holes. Nothing natural about a mouse being cornered either, and when it does happen the mice get even more violent when they see no escape. Frantic even in some cases.
The only reason I know of personally for feeding live is for the snakes that must have it because of feeding issues. IMHO