Well, I think it depends on what you're looking to achieve.
If your goal is to integrate Algerians, such that they are viewed as equals to ethnic French, then that is unlikely on a cultural/sociological level in the 19th and 20th Centuries. France was very much just as racist as its European and American compatriots, after all. However, if your goal is to integrate Algerians into the French system into such a way that Algeria remains part of France and, in the long run, can achieve a degree of integration on the first field, that's something else and more doable I think. I agree Britain and Italy could not absorb India and Ethiopia, but that's for demographics and distance if nothing else. The example of the United States and Native Americans is, however, a point against the thrust of your argument, and I think is rather applicable to Algeria for France.
Without question, Native Americans long struggled for acceptance and share a sordid historical story with the United States. Despite this, today the overwhelming majority of NAs speak English, are Christian and have (and continue to) serve honorably in numerous American wars. Despite the aforementioned past and continued issues into the present, there is no real separatist movement among NAs; can anyone seriously deny Native Americans are a less distinct culture compared to the original WASPs of America as compared to the French and the Algerians? As bad as race relations in the United States were in the 1930s, American leaders could see the realpolitik value of extending citizenship to Native Americans then. Another example in this vein I can think of is Hawaii, among others.