I get leaving the fruits of creative work for your progeny so they can have a buffer after you die, but I strongly disagree that the period should be the length of three human generations. My work should belong to my culture and my world after a decade or so, and really, a decade after publication, not after I die.
It is not natural to treat ideas like regular property. Some degree of ownership and control is needed in a market economy, but even for the life of the creator is excessive and stupid. I can create a cultural phenomenon, but unilaterally decide that it doesn't belong to the culture until 150 years after it was popular? Total bullshit.