Thanks to Hans for the link:
Speech by Richard Stallman at Cambridge University,
25 March 2002
You might have been familiar with my work on free software. This
speech is not about that. This speech is about a way of misusing laws
to make software development a dangerous activity. This is about what
happens when patent law gets applied to the field of software.
It is not about patenting software. That is a very bad way, a
misleading way, to describe it, because it is not a matter of patenting
individual programs. If it were, it would make no difference, it would
be basically harmless. Instead, it is about patenting ideas. Every
patent covers some idea. Software patents are patents which cover
software ideas, ideas which you would use in developing software. That
is what makes them a dangerous obstacle to all software development.