I was going to do this as a poll but as I also want you folk to give replies, lets's do this as a discussion topic and if there's sufficient choices, maybe a poll to decide what is the worse SF TV series based purely on inconsistencies that stretch even its own sense of belief.
For me, it has to be 'Space: 1999'. Although I can just about see the Moon being blown away from the Earth and even being flung to a more planet populated area of the galaxy via 'The Black Sun' episode, the errors just mount up from there. Probably the classic is Koenig asking Bergman about information about a planet neither of them could know anything about and getting a serious answer. Let's not even attempt to address how quckly they had to make the Moonbase Alpha's windows air-tight again after they opened them in one episode. I haven't even gotten to the second season yet.
Do you think my comments are valid or do you have a worse inconsistent show?
C'mon, what about something like that Australian SF 1960s series 'Phoenix 5' which went seriously down hill after its pilot episode.