The reasons for spread of memetic traits, I think, are so varied that they differ profoundly and incompatibly with the spread of “genetic” traits via natural selection, which has only one pathway: a trait spreads when it enhances the number of copies of the genes that produce it. In other words, you can reverse-engineer a Darwinian trait by studying how it affects reproduction, but you could never do that with “memetic” traits like music, words, the use of forks, and so on. Each one spreads by a unique pathway, compelled by unique forces.
Supposedly genetics has one pathway: enhancing gene reproduction - while memetics does not. However, in memetics, memes spread by enhancing meme reproduction (and longevity and fidelity, just like in genetics). The claim that this is somehow dissimilar from genetics seems unsubstantiated to me.
Yes, aerodynamics influences aeroplane memes, structure affects girder memes and principles from chemistry affect solar panels. However, similarly, aerodynamics influences gird genes, structure affects tree genes and principles from chemistry affect photosynthesis in plant leaves. There are similar types of "unique forces" in both organic and cultural evolution.
Jerry goes on to revisit the objection that saying that cultural items spread "because they are memes" is an empty tautology - that what we really want to know is the actual factors that make a cultural item spread, and this gets us into varied territory that lacks general principles.
However, the same objection was made against genetics. It was claimed that "survival of the fittest" was just an empty tautology. The classical response to this is to say that here "fittest" should be interpreted as meaning "expected reproductive success on the basis of the actual or expected phenotype". The exact same response applies in memetics too. Scientists have a range of theories about which memes spread and which do not.
Coyne apparently doubts the applicability of evolutionary theory to culture. However this is now well established and there's a large literature on the topic. I've read a lot of this literature, but I see no evidence that Coyne has got any further than "The Meme Machine". Coyne simply isn't familiar with the literature of the subject he is discussing. Others have also pointed this out.
Another issue is that Coyne seems to want memetics to explain why memes do better than others. However it isn't the job of genetics to explain why some genes do better than others. Instead, genetics addresses the details of how mutation and recombination operate. IMO, memetics has the same basic remit in the cultural realm: to explain how cultural mutation and recombination operate. Why some memes do better than others is the result of a multitude of ecological factors - just as is true with genes.
I think Jerry's technical objections to memetics fail. There aren't any credible technical objections to memetics - it's a perfectly sensible approach to studying cultural evolution. My impression is that this has dawned on many of those who study cultural evolution. Many of these folk have apparently given up attempting to find technical flaws in memetics. The most prominent meme critics these days are a bunch of non-experts who frankly don't know what they are talking about.