There have been several studies of tidally-locked planets around M-dwarfs which refute this.
Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and the Implications for Habitability, M. M. Joshi, R. M. Haberle, and R. T. Reynolds , Icarus (1997)
A Reappraisal of The Habitability of Planets around M Dwarf Stars, Tarter et al. (2007), Astrobiology,
Basically atmosphere and ocean circulation transfer the heat, and you get a relatively habitable earthlike environment.