Criticisms of the rationalist movement and Less Wrong have existed for most of its duration on various grounds.
The movement has been criticized as overemphasizing inductive reasoning over empiricism, a criticism that has been refuted by Scott Alexander.
Main: Roko's basilisk
The Roko's basilisk thought experiment was notorious in that it required specific preconditions available nearly exclusively within the Less Wrong community that rendered the the reader vulnerable to this 'memetic hazard'. As such it has drawn derision from critics who feel perception risk from unfriendly AI is overstated within the community.
Less Wrong's community was partially founded by soliciting users from the transhumanist SL4 mailing list and Eliezer Yudkowsky is himself a prominent transhumanist.
As such, the fringe nature of transhumanist ideas such as cryonics, AI and such has met with continued scorn from the sceptics based at RationalWiki.