I don't think the example you mentioned isn't similar, but it's a smaller part of the problem of Morgan Freeman's argument on 60 minutes. In your example with France and England trying to assimilate, the reason it failed is because the French and British wanted to keep their distinct identities. Had this not been an obstacle, then assimilation would have happened.
Whereas with black and white culture in the US, even if both cultures wanted to remove their distinct identities, there would still be multiple obstacles to keep complete assimilation from happening, the biggest being ethnicity and the differences in physical appearance. The Trayvon Martin flyer being posted in this thread is a perfect example of what I'm referring to. Trayvon Martin was killed because of how he looked by George Zimmerman who was of a different ethnic group. Had Trayvon Martin looked different/looked like he belonged in a different ethnic group other than black, he would probably still be alive.
Now of course most black people never deal with situations where other ethnic groups are trying to kill them, but the difference in black people's appearance and how black people can be identified as another ethnic group because of it plays a role in the daily life of a black person who is around people of different ethnic origin. Getting rid of black history month, BET, and black culture magazines doesn't solve this issue and assimilation will never happen as long as the way black people look and are treated because of that is still an issue and generally received as a negative (this negativity that's generally seen by other ethnic groups being the second big problem).
I know it looks like I'm downplaying your argument/examples, but I just wanted to explain that the reason many people dislike Morgan's argument goes beyond "pride" in ethnic identity.