I guess the question you'd ask is... are you bothered by MK Dons?
The difference is ones proving to be hugely successful, whereas the seemingly non-existant teams from Leipzig contnue to be... well... Non-Existent.
AFC Wimbledon have done amazingly well to get back to where they're at, and they've subsequently allowed MK Dons to be accepted.
This RB Leipzig have in theory, brought a Professional Football team to Leipzig, one who's doing quite well too, and whilst it goes against the traditionalists way, but why shouldn't they be accepted?
Bayer Leverkusen (It's in the name for christ sake), Wolfsburg and Hoffenheim are from similar ilk, so I guess the big question is, why the HUGE kick off over Leipzig?