Where do you disagree? Do you really think that Paul was saying that it is ok to sin in disobedience to what God has commanded as long as we are convinced in our own minds that it is ok? If I became convinced in my own mind that it is ok to steal something, would I be free to do that? Where God's Word gives a clear command, then human opinion must yield, but where God's Word is not clear, only then should we each be convinced in our own minds. If our conscience is not bothered by doing something that God said was an abomination, then that doesn't mean that we are free to do that, but that our conscience has become seared.
The reason why so many people do not understand what is said about laws in the Bible is that they fail to distinguish between what is said about God's Law and what is said about man-made laws, and erroneously take something that was only against man-made laws as being against obeying the Law of the God that were serve. If you look at Colossians 2:16 by itself, then it is ambiguous as to whether Paul was saying that they were not to let anyone judge them for keeping God's holy days or for not keeping them, but if we look at the context of the views of the people judging them, as well as keep in mind the theme that we must obey God rather than man, then it becomes clear:
Colossians 2:8 See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits[a] of the world, and not according to Christ.
Paul would not have described those who were teaching people to obey the Law in accordance with the example that Christ set for his followers as taking people captive by philosophy and empty deceit, according to human tradition, and not according to Christ. He went into more details about what these elemental spirits of the world are later in the chapter:
Colossians 2:20-23 If with Christ you died to the elemental spirits of the world, why, as if you were still alive in the world, do you submit to regulations— 21 “Do not handle, Do not taste, Do not touch” 22 (referring to things that all perish as they are used)—according to human precepts and teachings? 23 These have indeed an appearance of wisdom in promoting self-made religion and asceticism and severity to the body, but they are of no value in stopping the indulgence of the flesh.
So the Colossians were keeping God's holy days in accordance with God's commands, they were being judged by those who were teaching human traditions, self-made religion, asceticism, and severity to the body, and Paul was writing to encourage them not to let any man keep them from obeying God.