What not use "mixed responses" but "mixed response"?

Because a mixture contains a lot of responses.

Context:

Philosophy of science has historically been met with mixed response from the scientific community. Though scientists often contribute to the field, many prominent scientists have felt that the practical effect on their work is limited; a popular quote attributed to physicist Richard Feynman goes, “Philosophy of science is about as useful to scientists as ornithology is to birds.” In response, some philosophers (e.g. Jonathan Schaffer[1]) have pointed out that it is likely that ornithological knowledge would be of great benefit to birds, were it possible for them to possess it.