The animals argument is bad. We are animals and the idea is to refrain of our bad instincts in favour of the greater good most of the time.
That being said abolition of borders is a very bad idea, a very basic visit of human history will squash any misplaced idealism regarding that subject.
That also being said immigration is most of the time a good idea as long as you put a consideratr effort into integration for your newly minted citizens.
Now I realize most of those are opinions without substance, the idea is to realize where people push back and why before backing them up.