The thing about memes is that while they are to a certain degree selected for by humans if they are useful, they are more strongly selected for being memorable (longevity), likely to spread by people telling other people or on larger scales like advertisement or endorsement (fecundity), and the accuracy with which the ideas are replicated when spread (faithful of reproduction). I chose these traits to have analogues to biological evolution, and it's true that natural selection doesn't necessarily select for traits that we as humans believe to be "good" traits. A Nobel laureate or an olympic athlete with only one child each is blindly considered to be less evolutionarily fit than the high school drop out with six kids.
Useful memes obviously have the advantage of their practicality, but that doesn't compete with the memes that are simply more fertile. For example, if you have a plant that you want to grow more bushy, rather than taller, you can cut off the top of the plant to reduce apical dominance, which allows more lateral growth. This can be pretty handy knowledge, I used it the other day so that a basil plant would grow more leaves instead of grow taller. However, I almost never share this knowledge with anyone, because honestly, the opportunity doesn't present itself much. I'll tell a less-than-tasteful joke way more often than I tell people about this information, and I'm sure that the joke is a much more successful meme, despite being of less practical value. Slogans and catchphrases and jingles can have ridiculous longevities, and are spread widely through advertising. People reading this post will probably forget about the gardening tip I just gave before they forget that KFC is finger lickin' good!
A lot of people have also pointed out the power of the idea of "faith". From a memetic point of view, faith represents the rejection of all memes contradictory to its own meme. This makes the religious meme extremely powerful, as by its very nature, it demands that you reject all contrary memes. These memes are also spread all over, door to door, from country to country through missionaries, from one concerned person of faith to someone who hasn't really given it much thought, from parent to child, from television, radio, the internet. Almost every channel of memetic spread you can think of is used to spread the Word.