At least if exotics were brought onto a licence system the numbers could be observed.
I've seen this statement thrown around in a few discussions on this topic and it is utter rubbish. The minute you allow ball pythons, retics, burms, red tail boas, blood pythons etc to be kept in Australia there will be an increase in morphs being smuggled from the US and Europe to be illicitly added to local licenses.
When people look at it logically there are usually a few caveats that come out:
1) Invasive species - "Well we could restrict the list of allowed species"
Those not allowed will still be smuggled.
2) Diseases - "We could implement mandatory quarantine or restrict imported"
How long do you quarantine for reptiles??? There will still be a smuggling market for those that cant afford the expense or don't have an import license.
3) "We could restrict the list of allowed species to those already in Australia"
Those not allowed will still be smuggled.
On this particular topic I think the regulation bodies are closer to the mark than we are. We seem to be viewing this through rose coloured glasses because it is what we want. If we approached this more logically then perhaps a proper damage mitigation process could be implemented.
There may well be a compelling argument to allow the keeping of exotics, but a reduction in smuggling is definitely not one of them. The argument over mammalian and avarian imports also falls short as this right would be taken away if it could (it is far easier to give new rights to people then take them away).
There may well be a compelling argument against keeping exotics, but species invasiveness isn't one of them either. I think you'll find that Red Eared Slider and Corn Snake issues have come about because people have had no other recourse when they decide the risk is too great. How many do you think would kill their beloved pet rather than release.