No, it is not absurd. A writer can spend ten years writing a book, living in dire poverty the entire time. He can live in abject isolation and lose his health, he can sustain permanent physical and emotional damage from trying to bring one book or piece of music to life. If the work later becomes acknowledged as a masterpiece, of course he and his heirs should have the right to benefit from his unique gifts and his extraordinary sacrifices.
I hadn't even thought of copyright as a socialistic concept until Arthalion had mentioned it, but I'm inclined to think he's right, especially after your explanation.
The hypothetical writer you describe is a "taker", seeking government welfare in the form of a perpetual protection of his one idea. I don't feel sympathy for such an artist who has put all his effort in his art to the detriment of his basic needs, for the same reason I don't feel sympathy for young athletes who are banking on becoming the next great professional athlete in their chosen sport -- the odds of a "big break" for both are pretty small. You need to have a marketable skill as a fallback.
If an artist wants to use his art as his livelihood, he needs to continue to create. I would point to someone like James Michener as one example of someone who has done this properly. He wrote his Tales of the South Pacific, and when that was successful he poured his royalties back into his writing, so that he could continue producing successful works of writing. Even under the old copyright laws, he would have been able to make a fine livelihood because he kept creating.
The old copyright protections gave a reasonable amount of time for the artist to produce another work without the fear of starving in the meantime. 42 years (28+14) is plenty. The reason why heirs benefiting perpetually is absurd is because they undermine the basic principle: granting the heirs that privilege doesn't forward the promotion of arts and sciences (unless, of course, they create something THEMSELVES, and get a copyright or patent of their own).
Beyond this, masterpieces become such by virtue of being widely known -- they enter into the common good, a common societal patrimony that in turn promotes other ideas. As such, they should and must belong to everyone -- perpetual copyright prevents that from happening. Likewise, any degree of copyright stifles some creativity, thus there are "fair use" provisions that even supersede copyright under certain specific circumstances.