When the president of a school of medicine tells his graduates to let no one tell them how to ply their trade, he is not telling them to forget everything they learned and to do whatever quackery tickles their fancy. Not at all. He is telling them that they, with their knowledge, their qualifications and their diplomas, are now authoritative and are not to succumb to the whims of others who would impose their ideas on them. He is telling them to have faith in their knowledge and understanding, not to do away with it.
The same applies to Colossians 2:16. When Paul tells his astute audience, ^Therefore let no one act as your judge in regards to food or drink or in respect to a festival or a new moon or a Sabbath day ^ (New American Standard Bible), he is telling us that we are now authorities in these matters, not the general public nor casual hearer nor the leader or follower of some pagan religion. He is speaking to a learned group not to neophytes. The neophyte needs to establish a foundational knowledge in regards to food, drink, festivals, new moons and Sabbaths. Let us not be hypocritical, we do not start our education with a graduation speech.
2007 Jacques Gauvin