This article is from the Science Fiction Fandom FAQ, by Vicki Rosenzweig firstname.lastname@example.org with numerous contributions by others.
Depends on your definitions. I think of them as real because
they've been around for quite a while and make a fine breakfast
when buttered and accompanied by a cup of tea. Others insist that
nothing sweet can be a bagel, because who in their right mind would
put lox and cream cheese on a cinnamon-raisin bagel? Plain, garlic,
onion, poppy seed, salt, pumpernickel, sesame seed, and egg bagels
are definitely real. Blueberry, pesto, sun-dried tomato, and
cranberry-orange are newfangled impostors. Cinnamon-raisin is the
current borderline between the two, but borders do shift, and it's
becoming harder and harder to find a decent pumpernickel bagel.