While Space:1999 was certainly superior to UFO in the arena of special effects, I simply couldn't swallow the impossibility of the moon being blasted out of orbit. Another major Anderson traipse into physical law violations.
To be fair, most TV sci-fi were not "hard sci-fi" productions, and like the novels of old, used whatever was the most fantastic situation to excite audiences.
Lost in Space
suffered weekly violations, but the overall thrills of giant, one-eyed beasts hurling boulders, planets with smoke rising above its surface like a burning object within a oxygen atmosphere, and a ship with more interior than the exterior frame would allow (TARDIS, anyone?) offered a thrill some dry, "hard sci-fi" production would not.
It may something about the culture (depending on your point of view), but as far as 1960s sci-fi productions go, a film like 2001
--with so many of its technical projections based on real science and the budget to pull it off--was nowhere near as popular as Lost in Space
to the general population.