Why did Native Americans trade for guns?

When Lewis and Clark arrived in Oregon, the Nez Perce tribe (estimated population 90,000) welcomed them and began trading with the French for tobacco and guns. Why did it not occur to them that this new white tribe, while friendly at first, might be dangerous? The french appeared out of nowhere, with white skin and GUNS for trade, a technology far beyond what they had previously seen, and obviously deathly. Why were the natives not afraid? Seems like they MUST have known that this white tribe was potentially very strong and dangerous. Was their desire for the guns greater than their prudence? Where was the foresight?