lumping good and bad together; not distinguishing between good and bad; mixing the worthy with the worthless
Idiomatic expression criticizing the failure to differentiate between things of very different quality or value. Often used when someone treats everything as equally good or equally bad. The literal image is mixing excrement and miso paste.
That critic lumps the good and bad together, treating every work the same way.
It's not good to have an attitude that mixes the worthy with the worthless.
Also means lumping things together indiscriminately, but without the vulgar nuance of 糞も味噌も一緒. 十把一絡げ is more neutral and can be used in formal contexts.
A set phrase combining 糞 (excrement) and 味噌 (miso paste), two things that should never be mixed, to express the idea of failing to distinguish between good and bad. The exact origin is uncertain, but it is a traditional Japanese idiom.