It's a fact that longer wavelength/lower frequency light (e.g. red) penetrates dense gas clouds better than high frequency/short wavelength light (e.g. blue). It's also a fact that you require a less dense surface to capture and focus longer wavelength light (e.g. radio) which is why radio telescopes have holes in them and it doesn't affect the instrument. You could do radio astronomy with a dish made essentially of chicken wire, but you could not do optical astronomy that way.
My question: Why should a denser gas cloud be porous to long wavelengths and a less dense detector be opaque to them?