The "purity" of your group
There is a good reason to protect the "purity" of your group. But then again the world is so dynamic you could honestly say that nothing truly grows in isolation. And it will always be a struggle to balance how much you allow in, and how much you keep out.
The pros of allowing things into your culture is you may enrich them, the downside is you may lose control and end up losing something critical which defines your culture, so much so that you end up with no culture. Or a culture which fails to do what it is supposed to do. It is a global dilemma, Japan had this issue, We all have/had this issue, even Europeans had this issue. (eg. the influx of immigrants has totally irreversible transformed what is "British").
By African Holocaust