Different cultures have different reactions to other humans that are outside of the group. Some take aggressive stances, others practice a more welcoming approach.

The Sentinelese people react violently to outsiders, but many (maybe even most) first contacts of Europeans with various natives was peaceful on the part of the locals.

There's enough variation even in just the modern world that I'd feel comfortable saying that aggressive responses to strangers/outsiders is not inherent but a feature of some cultures.

Why it's in some cultures and not others is probably a very complex topic worth investigation.