The thing you're missing here is that a lot of people are not capable of reading the animals' body language. Hence, permit. Also the part where just taking some wild animal home as a pet isn't ok, and to actually care for one you would usually require some pretty specialized knowledge.

I also fully agree that dogs above a certain size should require permits because holy fuck I know most of them are pretty chill and at most kinda loud but they still scare the hell out of me and I can't trust their owners to control them in all cases. And while knowledge of how to handle them is more common, some people still fuck that up..