Well, I will argue that apology is necessary because the Cultural Revolution, along with the GLF, is the PRC's original sin against its own people (it is worse when such crimes are committed against its own citizens than the others). Both are events more and more educated Chinese consider wrong. You can compared it to white supremacy in the United States. It is also an original sin because radical Maoists today still embrace Cultural Revolution, just like the far-right elements of the GOP still believe in the Confederacy and white supremacism. When folks criticize the good old USA, the first things they come up are white supremacism and remnants of slavery. Meanwhile, when folks seek to delegitimize the CCP today, the things they mention the most are Cultural Revolution and GLF (of course there's 1989, but that's another issue under a different political-economic context).While some of these first generation private entrepreneurs were victims of Cultural Revolution, the others were red guards. Cultural Revolution was complicated. You often have both victims and victimizers in a single family. My family was victimized, and for many years we had former red guards coming and asking for our forgiveness. Some we forgave some we didn't (as a rule we refuse to forgive anyone with blood on their hands). What could an apology from the party do? Cultural Revolution was launched by Mao to wage war on the party and the government. Most people who later came into power were themselves victims of Cultural Revolution. Why do victims need apologies from other victims? Sometimes just moving on is the best solution.
Since the CCP beginning with Deng Xiaoping has officially declared the Cultural Revolution as a mistake (but refuse to mention it in textbooks or compensate the victims), it is now time to go further and confront this inconvenient part of history. By apologizing, it is not just about saying sorry, but also building museums commemorating well-known victims (like Liu Shaoqi, Peng Dehuai, Bian Zhongyun, Tian Han, victims of cannidbolism in Wuxuan in Guangxi, purged military scientists, or even defense projects - like the WS-6 engine - ruined, etc.) of mob rule, as well as maybe a memorial in Henan (say Xinyang, the largest epicenter of famine in 1959) for the GLF. Textbook should talk about what led to the failures of GLF and tragedies of Cultural Revolution, so student grow being aware of what is to be avoided. Just think about the African American museums in the United States. They will not eliminate white supremacism, just like radical Maoists will not be eliminated. However, these museums teach citizens to reflect on their country's original sins and vulnerabilities, and encourage informed debates.