RMS is Richard M Stallman (see Richard Stallman), a famous programmer in the GNU/FSF scene, but not enthusiastic about Tcl. (See Who says Tcl sucks...).
I think RMS is a grand guy. I think his opinion is based on experience with a very early version of Tcl. Richard tends to consider things in terms of their relationship to GNU, and to his own concept of Free Software as a philosophical imperative. Tcl has no particular relationship to GNU, so Richard probably does not think about it much at all. ;^)