And then one migt ask if these assumed similarities between "ideas" ("memes")and viruses are real or only apparent. Those who claim they are real please come up with some reasoning!
First of all, I don't see it as much more than a analogy that may bring an interesting perspective on cultural evolution, on how it may evolve "by itself" rather than being under our control, as may be perfectly intuitively acceptable.
The similarities with viruses are, that, like them, culture/memes are not in our DNA, you can pass your culture not only to your biological children, but to other people, it's called "horizontal transmission". It can also evolve in "detachable" parts, or modularly, instead of each cultural "entity", or whatever fills the concept of "meme" in more standard jargon, necessarily being more static/monolithic. As in a sort of "cultural creationism", where cultures are unrelated -- I'm not suggesting that the idea that culture evolves and has degrees of relatedness didn't exist before Dawkins meme meme. But perhaps the analogy might help understand how the internal "semantics" or struture of a culture may not matter much for it evolution. One could argue that a certain people that believe X could never had this concept from an Y predecessor because it's illogical from the Y paradigm, but seeing it in a more "organic" fashion it's more or less like saying that cats have an intrinsic "catness" that could never had evolved from a common ancestor of dogs. Perhaps it help us to see that some cultural changes could not have been so sophisticated as they might appear to have been based on the divergences; instead, it could be largely due to accidents of cultural replication, where the ancestral "paradigm" ceases to impose a constraint to the evolution of contrasting, but yet closely related ideas.
But perhaps more importantly that it can evolve "by its own", not necessarily because it's useful for us (as would be the expected misleadingly intuitive notion), but just because they "fool" us into reproducing them. The idea can be based on false or useless information, and yet, portray itself as something real and important, which leads to replication. Sometimes just uselessly, sometimes even harmfully.
That is, essentially a biological analogy with the fact that bad ideas can happen and can be highly popular despite of being bad, because being good is not a requirement for being popular, as could be a natural overestimated expectation for products of our minds.
One thing that often is used as a criticism against the concept is that it would be just some sort of detrimental comparison of religion with viruses, but it's not quite that. Not only it does not apply solely to religion, or solely to bad things, but for culture in general. And despite of being "viruses of the mind", religions can also be argued to have positive, "mutualistic/symbiotic" aspects, not being just purely nocive, independently of their fundamental statements about the supernatural being true or not.
Ironically, once I saw someone criticizing the concept, saying that it's a terrible,
virulent idea.