Everyone has characteristics that differentiate them from others. Whether a person is categorized by a common characteristic such as ethnicity, skin color, religious belief, or a smaller scale characteristic such as personal interests, or what type of car one likes is determined by how well we know them. Racism is not created by holidays; it is created by intolerance, and an unwillingness to accept people from other groups. When people have an opened mind about other people they will still categorize them by characteristics, but they will not discriminate against others based on appearance.
Categorization by characteristics can be a good thing, for instance without categorization we could not have cultural sensitivity and we could easily offend someone if we acted inappropriately. Furthermore, from an economic standpoint categorization helps us to produce the right amounts of products for the right number of people. Everyone is not the same and for people to treat everyone the same is to ignore their cultural and personal interest. Categorization (or racism in this case) is not harmful as long as our intentions towards others are good and we do not use it to assume something about another person's personality.
I still laugh when I hear someone call a black person in Africa an African American, or when people say "Happy Thanksgiving!" to people in China that have never celebrated the holiday. Who could fault them, their intentions are good and they mean no harm and should not be faulted for it.
Ultimately, all the trouble with racism, or cultural conflict, comes about in two ways. The first cause of cultural conflict is when a person or group's intent is to physically or verbally harm a person or people by offending a group that they belong to. The second is when people misperceive the cultural ignorance of others as having bad intentions. Although both of these circumstances come about often, when someone's motives are to cause harm is the only time people should take offense.