I strongly disagree with that. Television shows should give respect to the intelligence of the audience and not assume they have no attention span. Especially science fiction shows.
People who don't have enough attention span to listen to the second sentence probably don't like science fiction anyway.
And paradoxically, I agree with you.

There is much value in complex characters and such. But I think this can be done as a process of discovery. I just think it's easier to lure people in with something that's
initially simple to grasp.
Imperfect example from my youth: my first issue of
Iron Man. It was interesting but I wondered what was the deal with the woman in the gold face mask. But I got the basics: she was Tony Stark's girlfriend. Same with this Jack of Hearts guy: he was a good guy who fought alongside Iron Man. Jasper Sitwell: he had some issues, seemed to be a conflicted good guy. Etc., etc. The story was interesting enough to persuade me to read the next issue. Then the next. It wasn't too long before I understood all their backgrounds and motivations. It all got fairly complicated, with years of back-story leading up to that initial issue I'd read. If all of that information had been crammed into that one first issue, I likely would've drifted away. Too much like homework.
I really don't see television as being very different. I can't envision hoards of casual viewers getting hooked by a complicated back-story right from the get-go, is all I'm really saying. It seems to work for other types of series, but
Star Trek seems to be its' own animal in this regard, perhaps because of years of assumptions and unfair preconceptions. I don't think it's insulting to anyone, I think it's just giving them information in doses, rather than overloading them with what initially seems meaningless.
I've got a pretty healthy attention span, but I'm not about to expect others to go for all of this
Star Trek stuff the way I did. But if they stick around, they're in for a lot of fun provided they don't get scared off right from the get-go. At least that's been my experience.