That's not something I can explain easily. But you are right, it wasn't all France that made fun of Bretons, mostly neighbours (and Parisians). Bretons are also not the only "minority" in France, as I said.
That's what I was trying to say. South Italians can all claim partial Greek ancestry (that undeniable), but they are (and feel) Italian by nationality. My argument was that one should not confuse nationality with ethnicity, which is what JFWR was doing.National feeling and ethnicities are two things apart. The way I see it is that Southern Italians, though they may be closer to Greeks, remain strongly attached to the Italian national unity (more than the North notably).