Although he had roughly guessed the sequence of events, Leon had no intention of abandoning the plan to hunt the Bear Monster.
Indeed, it might be the abrupt changes in ecological balance that led to this fierce conflict between humans and giant beasts.
But regardless, this Horror Mountain Bear had already caused hundreds of deaths, and that was just the countable casualties from Leding Castle. If left unchecked, who knows how many massacres would follow along its migration path.
The Horror Mountain Bear is part of nature, but humans living on this land are as well. Both have the right to survive here.
Man eats beast; beast eats man. The struggle for survival is not a matter of right or wrong. Leon did not want to arrogantly place himself above nature.