You can, using the resulting output as insulation or feedstock for concrete. This is simply a more thorough solution.

When that concrete is later demolished, what new risks are we creating?

Grinding the blades to use as filler is indeed one of the downcycling routes currently in use for old blades. It is energy intensive and there is limited demand for the filler because it has to compete with other very low cost materials, so the economics are not usually favourable.