This is a big question, as it requires us to think very big to try to get an answer, much bigger than most of us are accustomed to, perhaps even bigger than folk like Feynman.
Dreaming up ever more devastating ways to destroy other members of our own species is absolutely not thinking big.
There seems to be a growing realisation that we are suffering from an illness of mind as a species, which limits our minds to activities such as above, and have done so for all of our known history.
We also appear to have a tendency to project this limited mindset on other species we would consider intelligent.
The tendency for us to feed on one another, and our planet in a giant pyramid scheme is not seen anywhere else in nature, at least amongst free creatures, and is unsustainable, a fact now becoming obvious.
Another fact of interest, noted by many scientists specialising in the area of genome research, is that our genome bears many discontinuities, similar to those which occur in things genetically modified, as it would appear if our genome had been tampered with many times, like domesticated animals.
Logically, aliens, if they exist, cannot suffer from the illness of mind we have as humans, otherwise they would have gone extinct before they could ever become interplanetary aliens.
So they are not profit driven.
A distinct feature of being profit driven is our tendency to cover up the tracks of it, to assist in denying the full extent of its effects on us, like an alchoholic hiding the evidence of our habit, denying the things we’ve done, and continue to do under its influence, including colonialism, slavery, and genocide.
That means changing history as we go along.
Hence we know very little of events before the more established religions appeared, which have all been affected to some degree or another.
Anything learned that might threaten the capability of continuing to operate in for-profit mode is automatically suppressed.
Hence we know nothing of any other way of doing things, as the ancient Egyptians, and aliens, might.
We interpret all events in terms of profit, changing all narratives, deleting and suppressing data as necessary.
In truth, the vast bulk of the knowledge we do have is not ours as individuals, it was gifted to us by our ancestors. All we can do as responsible individuals is to try to build a little on it.
That stands in contrast to how we actually operate, driven by profit.
We colonialise knowledge for profit, only sharing it for something in return, where possible.
Hence our education system.
Even government run education amounts to the same; we pay for it with taxes.
In truth, our urge to profit limits our capability to infinitesimally less than what we would be capable of without it.
We could be aliens too, if we were free of that flawed mindset, as aliens must be, if they exist.
If we try to put ourselves into an always giving mindset, rather than our usual deeply flawed always taking mindset, we get a tiny glimpse into how an alien has to think.
How would they think of humans, their descendents, stuck in this self destructive spiral of greed?
They would be keeping as low a profile as they possibly can, to avoid any possibility of them being instrumental in us pulling the trigger on this nuclear gun we are effectively pointing to our head as a species.
I think this is far more likely than Mr Feynman’s conclusion, clever cookie though he might have been.
My own grandparents had first hand accounts, together with many others, of seeing multiple alien spacecraft, in 1938, which were ridiculed by media and authorities at the time.