This notion comes from the idea that the most "sincere", "pure", and "real" expressions are those which arise spontaneously from the subconscious without any intervening thought, skill, mechanism, technique, or labor. The truth is quite the other way. Without the proper means (technique, thought, labor, etc.), the intended ends cannot be reached. Eliminating the means doesn't make the ends easier to achieve, it makes them harder or impossible to reach.
If you want to see "pure expression" without any skill or planning then don't look at modern art, listen to the screaming of an upset baby.
