With all due respect, I feel that you may be dismissing some basic concepts / fundamentals that man and nature have already established. Key cornerstones to the very foundation of evolution actually! Consider the following:
Ducks fly in a V.
Wolf packs travel at the speed of the elders...
Even in Le Tour de France.... The Peloton exists for a reason!
These are just a few examples, but if you don't want our squirrels then fine.
Why would Party A add
1. security risk
2. greater drain on resources
3. drama
4. etc.
For an unknown person or group who cannot provide security, food, or any other essential survival need for themselves? Even someone with significant medical skills adds no real value if there are no such supplies available, and most in that field will have zero experience in an austere environment.
Secondly, if a person doesn't value their own life, or the lives of their family members enough to have provided even a minimal safety net for misfortune or disaster....why should anyone else?