It's not "totally cool" to make up "holy days" and keep them. If you read Romans 14 you'll see it was a church that consisted of Jewish converts and Gentles, some of the members felt the need to keep elements of the old Mosaic covenant. The passage is not speaking about making up holy days and keeping them, but keeping days that belonged to a different covenant. Paul does give good advice concerning those who keep the holy days of the Mosaic covenant, "Let every man be fully persuaded in his own mind" as to their usefulness. I'm sure we are all persuaded in our own minds that Rosh Hashanah, Yom Kippur, Sukkot, etc. are no longer binding. After some reflection you will come to understand Romans 14 doesn't apply to the keeping of ChristMass.