Good god, if I know that you are Chinese, I won't start this conservation.
Firstly, the rape of Nanking happened long time ago. Most of the people involed in the event are dead or lost their memory because of their ages.
Secondly, I dont see it worthly to keep talking about it because there were many more brutal events happened in that world war and none of them did bring upon justice.
Thirdly, I would like to remind you that your civil war (demoracy & communism) had much much higher casualities than the war between your people and Japanese. I even dont want to talk about the cultural revolution that devasted your country for decades and killed zillion of good people and cultural hesitage in Chinese.
and finally, I dont care about gulf of Tokin or Napal bomb, really. Amerikas and Vietnamese are friends now and they are helping us to develop our country. It does not matter if Amerikas did kill gazillion of Vietnamese 40 years ago. Past is past, you know.
I know that Chinese culture really value the past. That's why there are many more Chineses who hate Japanese than any country that was occupied by Japanese during 1900-1945.
I'm not too familiar with Vietnamese culture so I can't make too much assessment on it as I would with Japanese and Korean.
Anyways, I suggest you read the hugeass lengthy one that I've written up there. It will explain "why" I "bring" it up and talk about it.
1. The reason I brought it up in the first place was not to re-condemn the Japanese. It's unproductive and a waste of time, not to mention doing more worse than good. The point is that it is an ongoing issue that we needed to solve, and solve as in not make the Japanese pay, but together both sides handle the past with a positive attitude that can put an end to it and let things move forth from then on. The attitudes of the denials are affecting the bilateral relationships and the overall image of the people in particular. There's more, but I've explained it up there. Go take a look.
2. Because those weren't brought to justice doesn't mean it's right, or that other incidents shouldn't. If no one ever speaks up and let things get away, it's as guilty as letting evil get away, or letting it happen. To let evil happen is to not do anything about it, therefore watching someone gets beaten to death is pretty much equivalent of helping it succeed, because no one is there to stop. The West are very double-standard in many things, particularly with war crimes and many other series of actions that they condemn others of doing. For us Asians to let them tramp our backyard and not speak up is EXACTLY the attitude of a defeatist, or one who submits to their will and feed into the stereotype that Asians are submissive and will never speak up.
3. I am fully aware, but as the focus at this moment is towards the Rape of Nanjing, this is where we're talking. And if you read what I've said up there, an example that I've made was regarding June 4th. As for Cultural Revolution, no denials there that it's the worst thing to occur in history. I do believe, and hope that the future China will face up to this past the way it should, and fortunately, there are NO lack of knowledge of this incident in China. It's taught in school, and it's too severe not to be talked of. Most people in China hates the government and their crimes, just so you know; they aren't that unaware as the biased Western media would like to brainwash others into believing. I'm also not from China, but from HK and Canada. I hope this explains where I'm from, and how it also allows me to see everything from the scopes of an ingroup and outgroup.
4. And while your point is valid that it's a very bloody event, what made it different was that when it's an internal thing, it's just sorting out inventory and cleaning out the closet, such as how Iraq put Saddam to death, or Gaddafi disposed by its own people. I'm not saying the killings were right, but the difference is equivalent of a fight occurring inside your household. It's your own family problem. You won't have each other for long, but if there's a need to get rid of the dictator when the time is right, you shall. However a massacre by external force, or an invasion, is different, where it's considered intrusion and entry by others. Similar analogy to why some Blacks call each other the N word, but it being said by others non-Black is unacceptable. Anyways when foreign factor comes into play here is where the bitter feeling goes extremely strong. This is why Chinese are so angry towards the Japanese, and this is especially because we Chinese are very pride-conscious, and we've considered all the humiliations since Opium War as the greatest wound in our history and our national pride, therefore we are very sensitive and conscious towards anymore infringement on our nation. To top it off, while the West stamped in before Japan, Japan would be considered the last/latest one in our minds, hence the recency effect. Coupled with the attitudes and the sensitive wounds, it flares up even more, and remains fresh. What I'm saying here is explaining why Chinese are so angry, and how while the earlier decades of instability were much more bloody, it's different from when Japan invaded. Another thing would be the aggressions from the colonization of Manchuria to the Rape, which spanned for quite some time.
5. Not meant to put cold water on you, but US also entered Indonesia the previous decades. The results were millions of Indonesians slaughtered, as ordered by the dictator, but advised by the US corporates(learned that in my first day of lecture). In the IR, it is all about Realism. As a student in IR minor and focusing on East Asia, I am all too familiar with what goes. US rarely do anything on behalf of friendship in IR; it's always about its benefits and what it can gain from it. You may say US is helping the Viets develop, but I'd truly advise you to look what happens if in the future Vietnam picks up in industrialization and wants more opportunities for domestic businesses to flower, while reducing/denying US corporations opportunities. You'll see what happens then. The US had toppled numerous democratic regimes in the past(merely because they do not support American interests), and even tried to install puppet dictators into states, including Iran (failed, hence the Iranian Revolution, and why Iran HATED US to the guts), and Egypt(Why Obama was quick to distance self from Mubarak). It's very tragic that too many people see Washington as really the Hollywood image they portrayed themselves as. Look at the economy today and how the US wanted others to bend down just to hold its weight, instead of itself going forth to fix the problems.
And just because they are your "friends" today doesn't mean they will remain so. In IR, it's always Friends with Benefits. The US in the past might be a bit more "truthful", but the contemporary one is extremely greedy and sinister. The world economy is screwed cause of them.
6. Past is past, but again I've said it up there with regards to attitudes of the past. If the US denied the incidents, then I'd think their "friendship" towards the Vietnamese people is shaky and should be questioned, for that will not be sincere friendship if to deny incidents like those. This is exactly why China and Japan's bilateral relationships aren't properly stable.
.If you ever teach in S Korea or China,they too will tell you they don't like Japanese.Koreans don't like the Chinese either.It's true,most Japanese look down on these 2 nationalities.They like to associate themselves with N Americans & Europeans & British Oceania's Autralians. 
