At the end of the day as has been demonstrated by both sides, this is just a matter of personal preference?
I personally find capitalisation of English names in a document unattractive, a bit 'shouty'; my use of lower-case is deliberate, and not the result of any laziness. I refuse to accept it is 'wrong', but equally I accept that the alternative view has equal merit. So can we just live and let live with this?
Where I think we have to be careful is the attitude to American spellings, which I think spills over into an unnecessary chauvinism. I can understand the desire to preserve British (and Canadian etc.) English spellings ('license' is my personal hate word), but we really need to move towards an international nomenclature for English names of birds. Great northern diver for sure sounds better to me than common loon, and there maybe isn't a lot of logic in splitting Stercorarius spp. into skuas and jaegers. But I'd be happy to use them in the interests of international communication. I might even be persuaded to use capital letters.
And before anyone points it out, I know we'd still have Dovekie in Clements and Little Auk in IOC...so obviously no easy answers...
I think there is at least one easy answer and its the same one as for scientific names: priority. That is to say, nothing named previously by the Old World should be fair game for the New.... no need for chauvinism then.