Memes replicate and survive or perish like genes, but the environment they have to survive in is the human mind, and the threat that they have to overcome is being criticized. One way to survive this is by being a good idea. So some memes are simply good ideas. But there are various ways a meme can dodge the attack that comes from criticism, and then you get memes that are trendy or holy or crazy or ideological. Since we're not perfect in our ability to criticize (what would that even be like? Sounds terrible) I think there's necessarily a hint of this anti-rational aspect in all ideas. But some of them go all-in on the anti-rational strategy.