The creator should have a monopoly on his work, within reason. If he chooses to cede that monopoly to some other power or entity, so be it. Let him use the law as he sees fit. This is one area where paradise will not issue forth. There is nothing unfair in allowing Disney and his agents use of the law to maintain profits from the creative efforts of Mr. Disney for an indefinite period of time, or to be extended as they might argue in court. People who want to make money off of Mickey Mouse can either shove off, pay royalties, or act under the radar with some risk.
It seems to me unfair that the invention of the corporation, the human creation of an immortal legal person, should destroy the way culture propagated all throughout human history before copyright was reified as "property" and people like you began advocating perpetual copyright held by such entities or passed down to heirs -- by remixing pre-existing cultural ideas, phrases, melodies, images. As Solomon noted in Ecclesiates, "there is nothing new under the sun." As more and more phrases, images, melodies are "owned" by such immortal legal persons zealous to collect rents on the "intellectual property", there less and less room for the creation of culture in the normal way, which always referenced pre-existing culture. Jazz would not and could not exist if your idea of ownership were applied by jazz musicians to their creations. You still haven't told me whether you really think that it should be harder to compose pieces like the Rhapsody on a Theme of Paganini or Fantasia on a Theme of Thomas Tallis because rightsholders have to be found and paid, or how that state of affairs would serve the Constitutional purpose of copyright.
Mickey Mouse should at some point become like the character of Robin Hood, the figure in Botticelli's "The Birth of Venus", or Beethoven's Fifth Symphony: something on which anyone can base derivative works, from which they can earn money if the market will pay them, without paying a "rightsholder" or being sued. So, yes it is both unfair and unconstitutional for Disney and his agents to use the law to "maintain profits from the creative efforts of Mr. Disney for an indefinite period of time" if that maintenance requires the enforcement of a monopoly on the creation of derivative works.
Disney has benefitted mightily from remixing pre-existing culture: Snow White, Cinderella, The Little Mermaid (Did they pay Hans Christian Andersen's heirs for the rights? No. The story was in the public domain, the normal state for stories, not locked up in some corporation's horde of "intellectual property"), Beauty and the Beast (They were really happy that no corporation was holding the rights to the works of Jeanne-Marie Leprince de Beaumont on that one), but try to remix Mickey Mouse and their attitude toward cultural appropriation from the past reverses.
You might ask yourself why the Founders didn't give Congress the power to grant perpetual copyrights, but specified "for a limited term". Get back to me when you've figured out the answer. Hint: it has something to do with Science and the useful Arts having a value beyond the merely commercial.