[snip]
For what it's worth, apparently genetic engineering in ST verse goes horribly wrong something approaching 100% of the time. It wasn't just incidental the primary examples went off the rails, but a consequence of the process itself, which is why it's largely opposed (apparently even after related technology advanced beyond that original batch). In-universe, you can probably blame it on Q. Though you can probably blame just about everything on Q, so that may be something of a cop-out :V
There
are some transhumanist elements that aren't strictly negative (The Doctor, la forge's eyes, data,
recovered borg, probably other stuff), but yeah, they don't get much attention. Probably mostly due to storytelling/audience concerns more than anything particularly intentional, if I had to guess. More trouble than it's worth (vis a vis that whole "profit" thing) to really work out how a cast of functional immortals would play out, basically.
Though now I kinda' want to see someone try that. I know there's been the occasional basically!immortal that's actually lived well-beyond-human-lifetime in sci-fi, but I can't recall of many that were part of the main cast, and even fewer that were particularly benign or relatable.
well, I can't recall any at the moment, but I'm pretty sure I've seen it once or twice