I think people often persists way too on this alleged "excessive stupidity" of the characters. I already talked about, this is the only arc, together with the Boo's arc, where such decisions are made motivated by the author. And no one has yet been able to give me a compelling explanation. On the other hand Mirai Trunks is perhaps the character that acting with greater discernment in all the manga. I think some have misread, or if they remember very little, and i don't understand what that means "aged horribly"..is still appreciated today. Paradoxically, I almost feel that there is some sort of "feud" between those who prefer Boo's arch and those who prefer this. I guess that I'm the only one to love them both.
All in all, it has its obvious flaws:-non-clash between Cell and Gohan (best in the anime);
-the entire final part of the Cell Games since Cell vomits 18 (forcing and objective and undeniable inconsistencies);
-lack of clarity about the apocalyptic future of Trunks;
-wasted potential on many factors (Togashi made me realize how it could have been even more fantastic a character like Cell).
Then, all'arcs have inconsistencies here and there, because Toriyama is a particularly not much careless author and, often, very forgetful.
However, I think that deserve all the popularity that holds, and the merits are: Mirai Trunks, Satan, Cell (specially imperfect),cyborg's humanity (this deserve more deepening) unpredictability and numerous twists and turns, Cell vs Goku, ndroid 16, partial use of nearly all the characters in the cast.
3. When Vegeta wanted to let Cell absorb #18, Trunks could've easily swooped in and destroyed #18 within seconds. Yes, it would be a somewhat cruel thing to do, but it would stop Cell from absorbing her, and he'd be easy pickings for the Saiyans. And to think Trunks was among the Z Warriors who had the most common sense.
This only in the anime, where Trunks has had several good opportunities to do this. In the manga he did not even the time to hit Cell: first Vegeta pushes him away with a kick, and after Cell blinds him with taiyoken. All this happens in a moment. In the manga, the arch have much more sense.