Yes, it's true that black cockies don't make particularly good pets (ie. they don't 'tame' as thoroughly as the white species). Having said that, though, I've heard of several RTBs which made brilliant companion animals and were able to learn small tricks. Despite this, though, the black species all do quite well in aviary situations and their collectability value remains high (ie. in proportion to their respective rarities).
And yes, the white species are *dreadful* pests in grain and fruit-growing areas, however farmers are gradually learning other ways of keeping them at bay (eg. using cut-outs of raptors or rubber snakes). While these birds are recognised as 'difficult' or 'invasive' species, they're still classified as wildlife and therefore come under all the same protective laws that other species do. So y'can't export them any more. Neither can you import a foreign-born bird.
In response to your final point, the white cockies and galahs were not pests during the times when the protection laws were enacted. In fact, I doubt they have actually been *declared* 'pests' legally, as that would require their immediate removal from any areas where they had been declared. The cockies' nuisance status has been a fairly recent phenomenon (ie. in my living memory) and grew slowly at first, gradually gaining momentum as the wild flocks grew and shifted in their distributions (reflecting growth patterns of cereal grains).
I'll ask around the ornithologists at our Uni to see if anyone has records on foodstuffs taken by cockatoos. My perception is that originally most species lived on native pasture grasses, tree shoots and fruits, changing gradually during the late twentieth century to a high dependence on cereal grains (notably wheat, oats and barley, but also including oil seeds like rape and canola). Don't quote me on that, though, as I have nothing concrete up with which to back it.
I've written this many times, but I find it fascinating, so will repeat it here. During my childhood, it was *highly* unlikely that one would see a cockatoo east of the Great Dividing range. As I grew into my teens, the occasional galah or SC2 would be seen. By the time I had children, these were not uncommon and Little Corellas were coming as well. Long-billed Corellas (like Hannah's Sunny) came later. Today, we see huge flocks consisting of hundreds of birds near the coast. Once, I even estimated over a thousand mixed SC2s with little and long-billed corellas on the playing fields at Newcastle Uni.
During my honeymoon (road trip north of Newcastle), my new husband and I rounded a corner on a country road and were literally stopped in our tracks by over a thousand galahs eating spilled wheat on the road surface. We simply had to wait until they had finished gorging themselves before we could proceed on our way. The birds were not in the least bit put off by our waving or the sound of the car's horn. We reckoned that was pretty bonza! (Fair dinkum: it was!) When the flock finally rose, the sky turned pink-and-grey for a few minutes as the birds headed westward toward the setting sun.
On a final note: much of Australia has been in the grip of drought for the past few years. Native birds are doing it *really* tough, as are our megabats, which are dying in their thousands from heat stroke and malnutrition. People have been helping by putting out water and fruit for the bats, but it will be very interesting to see the net effect of the big dry on bird populations.
