The problem with human technological capabilities is that we as a global society are able to have a huge impact on the ecosystem before we fully understand the consequinces. Even something that seems insignificant (like moving a few hundred rats from one continent to another for the pet trade) could have serious results.
On another note, I thought it was hilarious that Doth managed to smuggle five green tree pythons into the country by just wrapping them around himself under his shirt.