I am for transhumanism, but I believe that there is a limit to how much we can meddle with our own biological state. We want to IMPROVE our bodies to break the limits that they have. Unfortunately, some people don't understand that and think that replacing their perfectly functioning limbs with artificial, motor powered ones are better/they assume that.
It's a good idea to take vitamins, since they help your body function, right? Improvements in science allow us to take our bodies to a true limit, before we would have to replace said body with mechanical parts. Glasses, hearing aids, computers, and many other things make things simpler for us, but WE need to use them. Computers improve our access to information, so we can learn more. If we learn more, our brains have a larger amount of information stored in them. If you're born with bad vision, glasses will improve your eyesight. There is no reason why we shouldn't take advantage of this.
Now, there is a limit. If we were to replace our organs or limbs, it needs to be logical. If you're missing a limb, or that part of your body is dying, it is perfectly fine. If you replace your limbs when there was no initial problem, you are definitely doing it in an illogical manner. We want to USE technology to help improve our body, when we NEED it. Unnecessary modification to ourselves is useless if we won't take advantage/have the ability to take advantage of it. If you're going to replace your whole body with a machine, you've essentially turned yourself into a robot that can learn on it's own (they already built a robot that DOES learn on it's own, over in Japan).