Maybe the answer to some of these questions can be explained by looking at present-day trends in movement of peoples, and immigration from less developed to more developed countries? Pannonians, Gauls and Britons - at an earlier phase of the Empire - were all regarded as barbarian and uncouth, but within decades of annexation had become Romanised, and were considered citizens of 'Romania'. Indeed, after the third century this became a reality. The Germans, on the other hand, demanded a share of the Roman wealth and prosperity and a say in its government, and yet steadfastedly retained their own culture and language. This may have been seen at the time as taking, but not giving back.
A modern parallel could be drawn with regard to attitudes towards ( and by ) immigrant communities in Western industrialised countries. Immigrant communities who 'fully integrate' are generally tolerated by the host population, whereas immigrant communities who are seen as wanting to reap the benefits but not contribute or integrate are regarded less favourably. Take for example Stilicho, pictured on a 5th century diptych with his Roman wife, but sporting a very German style moustache, or 'Gothic Beard' as it was called then. It probably wouldn't have gone down well at all. And moving into the 21st century, it is notable that some European countries are in the process of attempting to ban modes of dress employed by immigrant groups who find it difficult, in several ways, to integrate with the parent culture.
Maybe the answers to some of these questions can be found by looking at present day communities in Britain and Holland, where certain immigrant communities are regarded with fear and suspicion, and others welcomed without any major problems? But this is all very delicate stuff, and one has to tread carefully!