In certain religions and cultures, other religions and cultures are looked down upon. This is usually why you would usually not see a democrat marry a republican, as their conflicting views in politics would override their relationship.
When someone is exposed to a culture they are not familiar with, they usually would not understand it and thus would not be comfortable with being in that environment. Although this seems negative, it is natural in many circumstances. In most cases, many people feel like they do not fit in with their counterpart's culture because they have not grown up in it.
