I wonder if this hints at an evolutionary adaptation at dealing with people outside of the in-group — could it be that there was an advantage to subconsciously perceiving non-native speech as a threat, or at least something worth being on guard for?
Maybe it's like music in some way. A cacophony is not unpleasant at all, when that's the majority of everything (tell me you're a death metal fan, without telling me you're a death metal fan), but when an otherwise clean and smooth rhythm or harmony is disrupted, it sounds extremely unpleasant. For a specific example, the intro to the song Cemetery Gates [1] practically ruins the song for me. It's such a beautiful and pleasant first 1:32, but then the dirty bit hits, and it's just too much. By contrast the transition at 2:31 is smooth, and so it sounds great and pleasant.
There was one thing, "the worse of them" and "worst than" that I think is a non-native error, that is so common, that it made me think it might even be some grammatical construct I never heard of.
seems like a missed opportunity to evolve the 'native' speech to something new
I like this. A missed opportunity to be conquered. I'm going to keep that one in my back pocket on account of I bet that sooner or later I'll be able to trot it out for some poignant drollery.