I have struggled with this question in my desire to keep snakes that are native where I live (and there is no regular source of captive-bred ones).
The problem here is that wild snakes are sometimes offered for sale by local people who have caught them out in the forest. There are very few predators of the adult snake here, so the main danger to them is from people, many of whom would kill them on sight.
The cons are:
If I buy them, I am directly encouraging the sellers to go back into the forest and catch more, reducing the wild population.
I do not like the general concept of taking animals that roam freely and putting them in a cage for my own amusement.
Although I try to take good care of my snakes, there are other people keeping them with very limited knowledge and care, and the majority die prematurely in captivity.
The pros are:
In good hands they can live a longer life than they may do in the wild.
By taking part in public demonstrations of handling and care we can reduce the fear of snakes and hopefully reduce the amount that are killed by people.
So far my compromise has been only to take snakes that were either long-term captives looking for a new home, or those born unexpectedly in captivity. I have never paid for, or sold, a snake.
I've had mine now for 15 years and we don't know their exact lifespan, but I have been wondering what I'd do if/when they eventually die. I hope that I would wait and see if I could find others needing homes, but that doesn't come up every day.
My principles say not to buy a recently caught captive for the reasons above - and I have, in the past, released snakes caught and brought in by concerned people who came across them accidentally.
So in general, I would agree with your brother and sister in law and say that it's not great to take wild animals and cage them. But the temptation would be very strong if I was faced with no other way...
