The difference is that some people actively argue that
the earth is
not a sphere, whereas those who argue that Paris is not the capital of
France so far have kept their activities secret.
If a fact is contentious, then it should be backed up with a cite.
How many religious fundamentalists does it take to
make a fact contentious? How actively do they have
to argue? Where are you going to draw the line? And
why should we privilege the points of view that
happen to be held by people alive today?
Wikipedia would be a parody of an encyclopedia if it
held that the approximately spherical shape of the
Earth is contentious. People expect an encyclopedia
to be written from a scientific point of view - and,
for the most part, that's how Wikipedia is written.
Regards,
Haukur