>Well, my personal view is that I can see absolutely no reason why a proper general artificial intelligence is not possible [...] - after all, we have an example of at least one kind of entity that displays general intelligence (i.e. us)

Very correct. We even have the source code. (About 700 MB worth of it.) Of course, we have no way of running it or an approximation of it, it is for a ridiculously complicated and massive parallel physical and biochemical computer following rules that we can’t begin to comprehend at any level. But we have sequenced the entropy that goes into it – so the existence proof is trivial. (As you indicate.)