Star Trek is...fascinating, to say the least, however with reference to modern technology and society's current limitations in the understanding of physics and the space-time continuum, your friend is quite accurate in proclaiming Star Trek to be unrealistic. However your friend failed to acknowledge that Star Wars, in the same respect, is also unrealistic in this current day and time.
Both the Star Trek and Star Wars franchises are constituent of the Science Fiction genre, which, by nomenclature alone suggests the blending of the "real" (Science) with that of the "unreal" (Fiction). For three dimensional beings, such as ourselves, it is nearly impossible to comprehend the 4-Dimensional concept of Space-Time and therefore the faster-than-light travel featured in each Science Fiction epic is a primitive however noble attempt at the display of "future" technologies, and therefore is *unrealistic*.
In the Star Trek franchise, given the number of stars that are estimated to make up our Milky Way galaxy (upwards of 100 billion), the existence of so many near-human alien species is unrealistic as the sheer weight of numbers alone would suggest vast diversity in the type and appearance of life-forms that could be encountered. However, lacking evidence of life forms outside of those found on Earth it is impossible and indeed impractical from a viewing standpoint to represent an alien species that is unfamiliar and therefore difficult to relate to.
The Star Wars franchise does slightly better in the diversification of alien species, however it too has shortcomings in certain aspects. Star Wars focuses more heavily on military action and combat. One of the more iconic pieces of Star Wars memorabilia is that of the Lightsaber. The lightsaber is undoubtedly an unrealistic if not altogether impossible weapon, as the dispensation of pure destructive energy being able to take and hold form without any type of containment field is,by societal standards, purely the realm of fiction.
Apropos of the existence of negative feelings harbored by the fans of one franchise against those of the other is unsubstantiated. Humans and their feelings are entirely illogical and, without the strictures of logic governing thought, the possibility of feelings that the human mind may conjure towards both Star Wars and Star Trek are myriad and often incalculable. There do exist certain humans that enjoy both franchises equally, and I number myself among these individuals. There also exist those humans who feel animosity towards the opposing franchise, however these feelings are often based off which series they were first exposed to, or simply which one they prefer.
However given the similarities that inherently exist between both Star Wars and Star Trek, to harbor negative sentiments against one franchise and not the other is illogical.
Live Long and Prosper \\//
The inviolable tenets of Logic