Or a much more likely: strong AI isn't possible.
Mind you, I think we are a long way off from actually having the theoretical or practical ability to build a true general intelligence - but I'm pretty confident we will get there eventually. Whether this development will actually turn out to be a good idea (Culture) or bad idea (Skynet) is another thing entirely.
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.)
Someone else comments that a person trying to take charge of a Culture ship is like a intestinal bacteria trying to take command of a person.
Edit: Of course, the Culture also appeals because of the much higher ambient humour level in the Culture than in the po-faced Federation.