Had a Kwanzaa discussion with the CSO and came up with the following analogy. If I'm wrong, tell me so.
Kwanzaa is basically like St Patrick's day. It sounds religious, but is basically cultural. It comes out of one culture, and sometimes involves things that people from another culture might think are sort of odd. (Green beer? Come on...)
If you're Irish, you can participate in St. Patricks day or not. That's between you and your Irish buddies.
If you're not Irish and you want to participate in St. Patricks day, hell, go for it. Just try to follow what the Irish folks are doing without adding too many of your own flourishes.
If you're not Irish and you don't want to participate in St. Patrick's Day, OK, don't, but there't no need to be an ass about it. Giving a big speech about how you think St. Patrick's day is "not a real holiday" in front of an Irishman is constitutionally allowed, but is really sort of stupid and really sort of rude.
If you don't believe in St Patrick's Day and a cheerful Irishman wishes you a happy one, just smile and say "You have a nice day, too, Sean!"
If you're Irish and think St. Patrick's Day is sort of dumb, and someone wishes you a happy one, smile and say "Gee, thanks!" They mean well.
Some UU churches, especially ones with Irish members, will do a service about St. Patrick's day.
If my church got a kick out of the St. Patrick's Day service, but asked me to do it every year because my last name was "O'Bannion," which it's not, I would probably get tired of it, but I'd try to be nice about it because, after all, they mean well.