When I say that when you adopt a mid-Atlantic accent to sing, it beats through my skull with the thunder of a thousand fire-hoofed stallions and makes me die inside each time I hear you, what I mean is you are perfectly welcome to sing with a mid-Atlantic accent if that’s where you come from. (Though if that’s actually where you come from, you most likely have fins and scales and your singing career is limited to being attached to a wood-effect backboard and animatronically booming Take me to the River to the delight of precisely no-one).
I am not against Floating Accent Syndrome of itself, because I suffer from it. Everyone who has lived for any length of time anywhere other than the place in which they were born should suffer from it. If you’ve lived in places other than where you were born, and don’t start to sound a bit Lucky Oceans, then you probably need to get out a bit more.
In short: If you sound like that, then sound like that. But if you don’t, don’t (cf. fire-hoofed stallions, dying inside, &c).