I just watched Susan Blackmore's talk at TED.
I believe that the true danger a meme (or gene, or teme) poses to the underlying replicator (organism, i.e. us) is that it can create a cascading effect that circumvents homeostasis.
By definition, every stable organism or ecosystem has a form of self-regulation that prevents catastrophic changes in state. However, just like a virus, a meme has the effect of perturbing the regular behavior of the replicator as it spreads among their population. Normally, the effects may be benign or inconsequential (e.g. a slight fever here and there, or some excess pollution that is quickly cleaned up).
However, certain types of memes (take consumerism for example) can perturb the ecosystem to such an extent, in such a rapid way, that its replicators' homeostasis is unable to cope with the change in time, to the extent that the system spins out of control. This is the catastrophe that is staring us as a species in the face right now.