This is a bit of a stream of consciousness, but I wanted to note my thoughts down:
Dennett's lecture partly relied on an analogy between what he called "ideas to die for" and the ant driving parasite. Part of the impact of this comparison was the idea that the parasite was a foreign invader, fundamentally separate from the host ant. The problem when trying to make a comparison between this relationship and the relationship between humans and ideas is that, in an important sense (perhaps the most important sense), humans are made of the ideas that drive us. They are not alien bodies invading us, they are us. Dennett seems to nod to this at another point in the lecture. I don't feel that the parasite is controlling me like an ant, I feel I am a collection of such parasites. It is not that the facts of what Dennett was saying were wrong, it is just that, after a bit of thought, I started to feel that a large part of the lecture's impact came from overstretched analogy between biology and the world of ideas. There seems to be a tradition of "social biology", in which biological science claims to bring deep insights into the study of human relations. Social Darwinism was a very influential manifestation of this. The problem though always seems to be that, in the end, all the biological model is is an analogy. It might prompt a bit of fresh thought, it might even be inspirational, but like all analogies it will not fit properly in some places. No amount of talk of ant driving parasites is going to itself give really valuable detailed insights into the nature of the Catholic Church, just as no amount of study of the Catholic Church will give new information on ant driving parasites. It seems trivially, obviously true that ideas/institutions/ways of thinking exist, just like anything in the world, because they have survived/replicated in the environment in which they have occured. Isn't that kind of obvious? Haven't we always known that? In this case, there is a lot of natural selection going on but there is also a good deal of intelligent design. So the analogy starts to stretch. If you want to get deeper into this you have to study ideas as ideas, not as analogies of biological objects, and that is what history, literature, political studies etc is all about. Presumably the interest in the biology of the ant parasite for the serious biologist is really in the detailed understanding of the interactions of chemicals, strategies etc. etc that allow it to exist and allow it to do what it does, rather than in the bald statements of the parasites existence that we find in Dennett's lecture . The same goes for an institution like the Catholic Church. The political/social analysis in Dennetts lecture was about as insightful as his generalised biology.