X years past the death of the copyright owner
VERY strong disagree; copyright should never have been expanded to it being "author's life plus ," and it shouldn't be normalized as OK. There was and still is a reason behind the rights ending merely 14-28 years originally - part of copyright in the constitution, to promote:
To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
Basically, it expired WITHIN the lifetime so the public domain had a regular influx of new material, and so that creators who would benefit from their copyright, would still have to create, which'd perpetuate the cycle of creation, and eventual public domain enriching.