I have argued the same in the past, during abiogenesis discussions. To me, once you start looking for a boundary, things get too fuzzy to sustain the assertion that one thing is alive (or, similarly, "complex" or "intelligent") while another is not.
Just take this lineup:
self-replicating molecule -> prion -> virus -> bacterium -> slime mold -> mammal -> human
Any attempt at drawing a boundary between two of those will find that they share enough characteristics to question the division. (IMHO)