Meh.Where Threshold became unraveled in my opinion was at the point that Paris abducted Janeway. Up until that point the story wasn't that bad. But the salamander procreating beings is when it became utterly absurd.
It's fiction, a major majority of most fiction is absurd.
Come, what are the chances that beings on the other side of the galaxy also find the representation of clowns frightnening. "Up The Long Ladder", we really believe that in the 24 cerntury that there would be people that would colonize space only to live like they were back in the earily 1900? That Data also has an evil twin brother? That poverty & war don't exists anywhere on Earth? That someone can create enough anti-matter to power a fleet of starships? We suspend belief for all of this but people turning into salamaders & mating is far fetched? It was nothing but a Trek version of "Altered States".