@trainedobserver, good question about whether there have been cultures who have wholly benefited from a more advanced culture absorbing them?
I suppose Native Americans are a good example in as much as to my knowledge at least, alcohol and firearms did not exist until Europeans arrived. The introduction of such accurate killing devices and the possibility of alcoholism and people acting differently because of alcohol, I think are pretty negative outcomes. However, this must be balanced against things like increased awareness of health issues, general knowledge of the wider world (I for one, would like to know about extraterrestrial life just for the sake of it, if nothing else). I imagine many native americans were happy to learn more about the world and universe that they may otherwise have not discovered for some time.
For our world culture as it exists today, outright contact with ET or at least definitive proof of having being visited is bound to have serious ramifications that are profound and long-lasting. There will be some positive aspects to this - possible new energy sources, understanding of the universe of the very large and very small are some I can think of right now -and there will undoubtedly be some negative consequences.
Personally, If we do learn for sure about ET life I think like with many things in life and evolution, it will be a question of adapt or die out. If we are anything as humans, we are able to adapt to new knowledge. Granted, sometimes only at the point of a gun or over a long period of time but the point is we get there. I strongly believe that barring any very sinister covert long-term action being carried out by ET right now, ET, or whatever seems to be the origin of UFO's and historical stories of Gods visiting us through the ages, would have acted already if complete annhilition were their goal.
In the main, it seems to me that our seeing UFO's is mostly coincidental, in that UFO's are going about their business anyway, regardless of whether any human is observing them or not and mostly they either do not care, do not even consider us worthy of interest or are deliberately giving us only glimpses in an effort to acclimatise us over time.
Religions and beliefs have fallen by the wayside regularly over the millenia and we are still here. Ok, maybe some Greeks and Romans were not happy to have their Gods fall from the lofty positions they were placed on BY HUMANS, but the sons and daughters of those people carried on living and breeding and their genes have continued to be passed on to the present day.
No doubt there have been some cultures wiped out by evil genocidal leaders of yesteryear but I think in the main, those that chose to accept the new way of life were allowed to do so and continue surviving genetically, if not culturally. We may have to do the same. And, to be brutal, anyone who just cannot accept a new paradigm such as the existence of ET and see that as cause to freak out and act out, leading to their incarceration, death or choice not to procreate will suffer the fate of any lifeform that fails to adapt. Maybe the Vatican's announcement that belief in ET life does not conflict with a belief in God was a very clever get-out clause so that if such a thing becomes fact, it will not lead to Catholics dying out, both as a religion and as people.
Life and evolution can be amazing and wonderful but of course can be ugly and brutal just as often. Those who survive a big change will do so because they were equipped to do so. It may be sad but some may just not be equipped to adapt to such a world-changing thing and I would not lose any sleep over anyone who resolutely fails to even try to accept such knowledge. I think the world can do without closed-minded people just fine.
There may be a bus coming along and it is up to every individual to choose to get on and go wherever it leads or stand still watching the rest of us do so. Word.