|You know it makes sense|
In 2006, a "remastered" version of Star Trek TOS was created. Some of this was purely due to technical considerations involved in transferring to HD. However, the project also altered the original by unnecessary changes, supposedly improvements, and it is these changes which are being discussed here. These included the addition of extra details and the alteration of special effects, notably in replacing the planets with more "realistic" ones. Although "realism" was a recurring justification, the replacement of models by CGI often resulted in a worse appearance than the original.
But don't modern audiences expect better special effects than TOS had? Yes, of course, if they are watching modern productions. But to expect them in old film and TV makes little sense. And it isn't possible to turn the whole of TOS into a modern production. What the changes do is to create inconsistency, with bits and pieces of high-quality special effects distributed in a 1960s TV programme.
Colourization, which is often dissed, actually makes more sense. It creates a consistent new artefact that can be easier on the eyes. All the same, you wouldn't colourize Casablanca or Citizen Kane, because they are so much works of their time that altering them would be a loss rather than a gain.
This is all part of a wider principle in art. To understand and appreciate a work of art, you take it in its context. We don't "improve" medieval paintings by trying to add in perspective that the original painters didn't.
There are inevitably comparisons to be made with the revisions of Star Wars, which are widely criticized. George Lucas justified these on the basis of doing what he would have liked to do originally if the technology had existed. The trouble with this is that every film is the result of compromises and multiple decisions, and if he could have done everything he wanted then, there would have been a quite different film, not just a glossier version of the same film.
Furthermore, the limitations of art are an important part of its creation. Several of the most interesting aspects of Star Trek were originally conceived as ways of coping with limitations: most obviously the transporter, which solved the problem and expense of having to show a ship landing and taking off each week. On a smaller scale, in "Where No Man Has Gone Before" (TOS), when Gary Mitchell develops godlike powers his eyes glow and he tilts his head back in a creepy and threatening manner. The glowing eyes were done with special contact lenses, and he was tilting his head back because he couldn't see otherwise. If the producers had been able to do everything we can do now, with CGI and so on, none of this would be there.
In both cases the real problem arises when the original version is not equally available. There is no harm in having extra versions available. You should watch what you enjoy. But do try old films before you reject everything that doesn't look like last year's output