The problem with counterculture is that it encourages people to uncritically accept that mainstream culture is horrible (e.g. boring, White, materialist, racist/sexist/homophobic) and must be rejected.

While everyone feels this way on some issues, counterculture encourages people to turn a dissatisfaction with some aspects of mainstream culture into a total rejection of it. And it does so not by rational argument, but by exploiting people's desire to feel special and enlightened.