One reader of this blog has made some remarks on Galatians 4:8ff regarding the applicability of those verses today. Granted, Paul was originally chastising the Galatians for keeping Jewish feast days and practicing circumcision, Jehovah's Witnesses still make the argument that the apostolic words apply in an a fortiori sense. If the Galatians should not have been observing Jewish festivals which were once commanded by God through Moses, then how much more should they and we eschew festivals/holidays that have pagan religious connections.
Some might feel that holidays are a matter of conscience. But how can the observance of days rooted in pagan religion be a matter of conscience for the Christian believer? 2 Corinthians 6 teaches followers of Christ to flee from idolatry and [spiritually] unclean things. The best evidence we have from historical sources is that the ancient Jews and the early Christians did not observe holidays rooted in pagan religion. Augustus Neander and others have documented these points.