I've never really given much thought to it, and I wouldn't actually call myself a "transhumanist," but I really don't have a problem with transhumanism. Using technology to improve ourselves and our abilities isn't a very controversial idea to me, but then, I wear glasses.
There are ethical concerns, to be sure, but I'm not certain how much they actually apply to things like cybernetics and bionics. We are already increasingly electronic; how many of us carry around smart phones and Bluetooth headsets*? I think we're a long way away from implants and replacement parts, but these attachments and accessories are a pretty close approximation. I'm not sure how much advantage there would be to a Bluetooth implant (for instance), aside from perhaps greater speed, but I know such concepts are in development (and there are some--like that sonar sensor--which do seem quite useful). And I'd be hard-pressed to see the significant difference between bionic limbs and some of the prostheses we have now. Sure, they're more advanced, and they may eventually mimic things like sensation, but morally and ethically I think they're pretty equivalent.
The real risks come from genetic modification, because there's a slippery slope toward Gattaca and similar eugenics nightmares. That being said, I'm a major proponent of GM with respect to crops and research, and I don't see any problem with the basic concept of applying it to humans in order to eliminate debilitating congenital defects and diseases and to extend and improve the quality of life in general. Obviously there would be details to hammer out, and there would be people who would abuse or try to abuse it, but the minor sorts of modifications that would be realistic and researched would, I think, present very little in the way of ethical issues.
Regardless of the realities, though, the idea that such modifications would result in a loss of humanity (and further, that such a loss would be generally undesirable) is very common in sci-fi, and particularly so in cartoons. I suppose that it's so common in children's stories because it's not only easily understandable, but it's also fairly uncontroversial (largely because it's fairly unrealistic, always a few decades away from any real relevance). It's hard to find stories involving cyborgs or other transhumans that don't either paint the modified characters in a negative light or explore the "machines dehumanize" moral. The only cyborgs I can remember in ThunderCats were the villainous Capt. Cracker and the Berserkers. He-Man had a few (Snout Spout, Mekaneck), but never even acknowledged that they were cyborgs in the cartoon** (as far as I can recall). Examples of this happening in the minicomics (Extendar is a notable example) were generally presented in the same negative, dehumanizing light. She-Ra's protagonists were almost universally the agrarian Rebels, while the only arguable cyborgs (such as Hordak) were members of the industrial Horde. This has always been an aspect of Cyborg's character, so naturally it was dealt with a few times in Teen Titans. Coldstone in Gargoyles suffered from this (also, he was a bit of a Frankenstein's monster), and there were similar sentiments in the Pack when Hyena, Jackal, and Wolf went in for cybernetics and gene splicing. This trope even shows up in some pretty unexpected places--like Transformers. I'm specifically thinking of "Autobot Spike," where having his brain downloaded into a robot body (albeit again, a pretty Frankenstein's monster sort of one) makes Spike violent and crazy. Even more bizarre is how this trope was a bedrock theme in Beast Machines. This one-sidedness is made all the more strange by that other staple moral of kids' sci-fi, that robots are people too. Just about the only
So given the generally negative attitude sci-fi, and children's sci-fi in particular, takes toward cyborgs, it's refreshing and surprising to see SilverHawks turn the trope on its head***. Not only are all the heroes cyborgs, but for the most part, only the heroes are cyborgs. Of the villainous leads, only Mon*Star could reasonably be called a cyborg, and that's only when he's powered up by the apparently mystical energies of the Moon*Star.
I don't know if the "dehumanizing" theme ever comes up in the series, but I doubt it--the series' belittling tagline (quoted in the post title) notwithstanding. I seem to recall the twins' bionic hearts coming up once more later on, but I don't think it's in that sort of negative context. "The Origin Story" treated the bionics as a routine necessity, not entirely desirable, but also not ethically troubling. I'll certainly be keeping an eye on this theme as I continue this series, but it's interesting to see a kids' cartoon--from an era where depth wasn't exactly their strong suit--bucking the general trend of popular science fiction.
*I don't, but only because I don't want to be turned into a Cyberman.
**This may make He-Man, then, one of the most progressive shows with regard to transhumans--that their conditions are unremarkable, except inasmuch as they give them superpowers. Alternately, it could just be that Mekaneck and Snout Spout in their ilk were very minor characters who only appeared in a tiny handful of episodes.
***The only other series I can remember that had major cyborg heroes were Bionic Six and C.O.P.S.--with only one hero (as I recall) in the latter case.