Not quite true regarding a RAS as you then become the RAC responsibility and have to comply with his instructions when flying IFR in class G with a RAS.
Not so! That's why it's termed Radar
Advisory Service. You are expected to follow the ATCO's advisory headings whether VMC or IMC - and are expected to be able to accept headings which will take you into IMC.
The only time you are obliged to follow ATCOs' headings is when under Radar
Control.
And yes, those of a suicidal mind who trust in the Big Sky theory may indeed quite legally fly IMC in Class G airspace without speaking to anyone.