OK ... In the spirit of returning to the original theme(s) of this thread ...
I agree with the sentiment and warnings Hawking expressed, but I can't say I agree with the way he framed it ...
IMHO the biggest issue relating to alien contact is whether or not we (humans) would recognize it as a contact in the first place. The reason this is an issue is the same reason why the notion of
any presumptive scenario (and response on our part) has to be qualified with respect to a major bias.
We humans, generation after generation, have considered ourselves the 'crown of creation' - i.e., the superlative end product of earth's history. The fact that prior generations have consistently demonstrated they didn't deserve such a self-attribution is a heavy clue that we've been deluding ourselves as to how great we are.
I mention this because the 'crown of creation' conceit is but one facet of a deeper bias - i.e., the notion that all things everywhere correlate with what we (think we ... ) know and how we see ourselves. Early cultures tended to project human-like qualities onto inanimate objects (animism) as our earliest form of explaining nature. Later cultures abstracted things, but remained firmly rooted in the homo-centric bias, by shifting to human-like gods and / or other folkloric and mythic beings that always seemed to resemble ourselves. Sure, we abstracted even farther to a single omnipotent super-figure, but we still claimed we reflected its / His form.
We can't help but project our peculiar nature, history, and experiences onto all notions of what it's like to be an apex entity - whether it's in the context of a single society, an individual planet, or the entire universe.
The two things we congratulate ourselves for (and which are cited by the OP) are:
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Advanced status - most typically with regard to technical prowess and products, but also secondarily with regard to 'maturity' or elevated outlook.
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Intelligence - almost always encrusted with the same loosely defined connotations and misleading spins we attribute to that quality in humans - i.e., a capacity for rational / logical thought and accumulation of technical / scientific knowledge.
... both of which are framed in familiar human terms that we project onto the notion of 'aliens' just as we've always consistently projected our contemporary self-constructed vision of ourselves onto most everything else.
My point is that we assume any alien species that is capable of interstellar travel must be 'advanced' and 'intelligent' on our own terms. Granted, this is the only basis we have for speculating about such things. However, we've proven ourselves wrong repeatedly over the centuries, and there's no particular reason to assume we're any less self-deluded now than at any time in the past.
Whether you're talking about medical experimentation, kidnapping, slavery, or armed conflict, the dangers we see in alien contact are unavoidably of the same nature as what we humans have done to each other for millennia.
It's important to look back at Hawking's standard illustration for the dangers - the arrival of Europeans in the New World (Americas). Yes, the arrogant Euros eventually overwhelmed and subjugated the native populations through deliberate actions and technological advantage. However, the single most important factor in achieving this subjugation were the diseases introduced by the newcomers - diseases their own best 'science' couldn't explain or reliably treat, and whose causes were microscopic life forms they didn't even know existed. Wells'
War of the Worlds wasn't 'won' because of human bravery or military prowess - it was 'won' by bacteria.
There's no solid reason for assuming aliens would be anything like us - either biologically, technologically, psychologically, or culturally - except for our own arrogance. As a result, the more pressing problems to consider aren't what human-like atrocities the presumptively human-like aliens would perpetrate, but rather:
- whether we'd recognize any arrival / presence / 'contact' in the first place;
- whether any such contact would necessarily induce any sort of conflict of the sort we perpetually undertake in such situations;
- whether any conflict or power struggle would necessarily be decided by the same means as we humans consistently employ to resolve our own differences; and ...
- how much more 'advanced' and 'intelligent' must we become before we can reasonably envision what the possibilities may be once we can shake off our self-reflecting biases?
Not hard at all ... We humans are the original, most effective, and most masterful antagonists to have done it to date, and I predict no other species will ever surpass us in this regard!