So - they had temporal drives since the 23rd century and, instead of perfecting them in order to function properly, they abandon this technology with enormous potential after the first try.
And why in the world would starfleet risk a constitution class ship with a crew of hundreds for the initial testing of such a new technology?
Gee, if only somebody would write a book exploring those very questions...
Well then, let us see just how coherent an explanation you will come up with.
They had genetic engineering for hundreds of years and don't use it - I'm not even talking about making augments, but about treatement of a variety of diseases and yes, lesser enhancements.
That's incorrect. We know that Federation medicine does employ genetic therapy to cure disease; see "Genesis," where Dr. Crusher uses gene therapy as a routine medical treatment for Barclay (though it goes seriously amiss), and "The Raven" and "Imperfection," where genetic resequencing was used or proposed as a therapy for problems arising from Borg implants in Seven and Icheb. And in "Doctor Bashir, I Presume," Bashir states that "DNA resequencing for any reason
other than repairing serious birth defects is illegal" (emphasis added), so it is explicitly legal and used in cases where there's a medical basis for it. (And we know from the Augments trilogy on ENT that in the 22nd century, genetic research was banned even as a treatment for critical illnesses, so clearly the restrictions have loosened by the 24th century -- and we did see the UFP engaging in genetic augmentation research in TNG's "Unnatural Selection" (though that was written before the ban on gengineering was retconned into the series).
"DNA resequencing for any reason
other than repairing serious birth defects is illegal"
This means genetic resequencing is illegal in most cases in which it would be needed (anything that doesn't involve SERIOUS birth defects).
For one thing, it means that, as per federation law, Crusher and the Doctor acted ILLEGALLY in "Genesis", "The Raven" and "Imperfection" - these were NOT serious birth defects-related cases.
They had access to parallel universes and don't use it.
Do they? Access to the Mirror Universe in Kirk's time was a freak event that couldn't be replicated. DS9 introduced a technology for beaming between the Prime and Mirror universes, but there's no indication that it allowed access to any other timelines.
Starting from the incident from "Mirror, Mirror", the mirror universe terran empire/memory omega managed to create the interuniverse teleportation technology.
The federation, despite having vastly more resources than memory omega, failed to do so - it even failed when having the DS9 interuniverse teleporter device. Highly unimpressive.
Alternatively, the federation did manage to create an interuniverse teleporter device, but choose not to use it, despite badly needing new technology.
As a couterexample, see Memory Omega, which, despite consisting of only a few tens of thousands of people, gained a technology FAR in advance of the federation's in the same timeframe by travelling to parallel universes.
And we don't know how much theft and other ethical violations they may have committed to obtain those technologies.
But we do know the results of memory omega's activity and the federation's incompetence:
Memory omega practically single-handedly ended the misery that was the alpha/beta quadrant mirror universe.
The federation managed to utterly fail its citizens, by failing to obtain technologies that could stand up to the borg, despite knowing it'll be coming and despite knowing of quite a few sources of such high technology (shedai data, parallel universes, artifacts gathered by named crews during the various series, etc). Result: 64 BILLON dead; the federation - a second-rate power.
You think Memory omega's activities are 'immoral'? I disagree.
Only the most rigid moral rules - which apply badly to real-world situations (AKA they only mamage to create suffering and more suffering) - can allow one to reach such a conclusion.
That this federation actually values exploration is a curiosity - or rather, a contradiction inserted by various scenarists and writers into the federation philosophy.
You do know, right, that the phrase "To explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before" was written
before the original series premiered in 1966, right? To the extent that there is a contradiction between the values of exploration and caution in the portrayal of the Federation, you've got it backward about which is the core philosophy and which is the later insertion.
The chronological moment of the insertion does not matter.
The fact is, the federation's dark ages attitude towards scientific/new knowledge is at odds with its penchant for exploration.
And, as various episodes/books made clear, this medieval attitude toward knowledge is deeply ingrained into the federation's psyche.
Sho is partly correct about the reasons these cultural/technological blind-spots were intoduced as part of the federation mind-set.
The other part is - when writing specific episodes/books, the scenarists/writers did not consider such things; they didn't consider such wider implications of what they were establishing.