This came up as a question in the Sunday school.
Interestingly, after searching online, I came across this:
Martin Luther: Pro-Christmas
Zwingli: Anti-Christmas
Clavin: Neither for nor against
According to the article, it's all about the difference between normative vs. regulative principles. Normative: It's okay if Bible did not mention (or forbid); regulative: It's not okay if the Bible did not mention.