SETI has occasionally been the target of criticism by those who suggest that it is a form of pseudoscience. In particular, critics allege that no observed phenomena suggest the existence of extraterrestrial intelligence, and furthermore that the assertion of the existence of extraterrestrial intelligence has no good Popperian criteria for falsifiability. Science fiction writer Michael Crichton, in a 2003 lecture at Caltech, stated that "The Drake equation cannot be tested and therefore SETI is not science. SETI is unquestionably a religion."
In response, SETI advocates note, among other things, that the existence of intelligent life on Earth is a plausible reason to expect it elsewhere, and that individual SETI projects have clearly defined "stop" conditions. Concerning the latter argument, the justification for SETI projects doesn't necessarily require an acceptance of the Drake equation. The search for extra-terrestrial intelligence is not an assertion that extra-terrestrial intelligence exists, and conflating the two can be seen as a straw man argument.
In 1983 Stanislaw Lem somewhat disappointed with all the efforts and huge investments which went into the SETI program has noted that the Universe is silent and he called it silencium universi.