While I have a similar story to Kevin's above, I won't go so far as to deny anyone their loathing of this episode.
I was a teenager in high school during that first STAR TREK season. Elsewhere I've mentioned that I was conflicted about watching this new sci-fi series or sticking with my tried and true BEWITCHED comedy, and that often I'd watch half of STAR TREK and then switch to BEWITCHED.
By mid-season, ABC had moved BEWITCHED up a half-hour to 8:30 and followed it with another similar comedy that I also liked called LOVE ON A ROOFTOP. So in the latter half of that first season, I was driven farther away from STAR TREK, now missing all of the episodes.
One of my lunch-room buddies in school and I used to discuss some of the TV shows we watched, and we were both drawn toward science fiction. And he was watching STAR TREK all along. The day after "The Alternative Factor" aired, I recall him telling me just how fantastic the science-fiction ideas were in this show, with positive and negative universes and how they were clashing in this episode.
Well, in those days before DVRs and VCRs, you watched what you watched - and missed whatever else was on, so there was no going back to see this show. Still, I filed it away in my brain, and the very next week, I abandoned BEWITCHED and LOVE ON A ROOFTOP and gave STAR TREK another try. I'd also read in that next week's paper that the next episode would be a good one for fans of THE TIME TUNNEL (which described me to a tee). So eagerly I watched "City On The Edge Of Forever" and became totally sold on STAR TREK and watched it through it's first season summer reruns.
It wasn't until STAR TREK went to syndication though that I got to see "The Alternative Factor" for the first time. And I enjoyed it, and still enjoy it today, even though I see its weaknesses with more adult eyes and with the 20/20 hindsight of understanding the episode's history.
Harry
Great and familiar memories, only at various times in the early 70s, the syndicated TOS would run at 8 PM, at the same time some favorite first run network series were airing. TOS usually won out, as it was just that much more of a creative draw.