@SaiDiaSWhile I get what you're saying, I think this falls under the same logic as discussions about genre.
From the point of view of what is actually possible in the real world, science fiction, fantasy, space opera, horror, and the supernatural are all basically the same thing. They take impossible and generally unbelievable ideas about the world and explore them as though they were real.
In literature, however, these are all separate genres because readers of these books expect different things in terms of plot, settings, character archetypes and development arcs, and so on.
The same applies to noncon, reluctant, coercion, and other tags in erotica. Of course they're all rape in the real world. But in written erotica, audience expectations about a story that includes reluctance are very different than a story involving rape.
None of this means that you should necessarily read a story that has tags you don't like, just that these tags serve a purpose for readers that is distinct from what the words actually mean in real life.