Do we equally criticise the children of Frank Sinatra for holding and enforcing copyrights to his songs, what about Walt Disney, or the widow of Dr. Seuss. Why are the descendants of Martin Luther King singled out, but not those of other culturally popular works? Whose works do we get to morally appropriate and shame people for not giving away for free?
Personally, I might blame the descendants of Disney the most if they had significant voting shares in Disney Corp, but as to the rest I doubt played a key role in the expanding copyright to the degree it has today.
I think we can really blame Disney here as well, but the really terrible thing is that the 'benefits' are not even accruing to Walt's descendants, but to shareholders of the corp.
I personally think that children shouldn't have any rights, and ideally copyright would expire after a reasonable time (not even for a creator's full lifetime, and certainly not after their death). However, it seems more reasonable for those rights to be held by the creator's descendants rather than a publicly traded corporation.
Personally, I might blame the descendants of Disney the most if they had significant voting shares in Disney Corp, but as to the rest I doubt played a key role in the expanding copyright to the degree it has today.