You can take fiction seriously without treating it as representing some sort of quasireality from which coherency across decades of story telling from multiple generations of story tellers is expected. Two story tellers having contradictory accounts of what happens with a fictional character shouldn't cause distress or consternation to people who enjoy stories about that character; people who enjoy fiction should be able to take that in stride. The whole premise of a "canon" to fiction is actually an artifact of the legal construct of copyright; with folk stories which exist outside of copyright the premise of a consistent canon isn't talked about because anybody can make their own story, many people have, and everybody accepts that the stories are judged on their own independent merits rather than their conformity to the supposed canon. With franchises under copyright though, it is the copyright holding entity which is, by people who "take fiction seriously" as you put it, granted a special privilege to determine the relative validity of different works written by different people. This isn't even a privilege given to the writers, as seen in this case where the privilege is assigned to the Paramount corporation; not to the original writers of Star Trek, nor even the writers of the show supposedly erased from the "canon". See also, the demotion of Extended Universe in the tiered canon of Star Wars by... who? George Lucas? No. The EU writers? No. By the corporation who bought the legal rights to Star Wars decades after most of that stuff was written.
It's not fiction which you are taking seriously. It's copyright. Canon in fiction is an expression of territorialism from the entity owning the legal rights, not some sort of intrinsic attribute of the collection of stories.