If they have said specifically not to go on their land, why are people still playing on it? It doesn't make any sense.
Just looking it from the outside, it would seem like people:
a) Don't know
or
b) Don't care
I've never been to Fuji or seen it (up close, at least), but it seems like it's decent to play at. That aside,
EVERYONE HAS SAID THAT PERMISSION HAS NOT BEEN GIVEN AND THE FIELD IS A NO-GO! There's a pretty good reason why everyone discourages playing there.
We aren't a bunch of kids running around with spring rifles or nerf guns. We're all a little better than that. We also need to take the sport more seriously and consider the image we are portraying to the public. We don't want to become a problem for the police or be know as people that don't respect and follow the law. As has been said before, we are all involved in "a fringe hobby", which means that any incident can reflect badly on all of us as a whole. We have to be responsible with what we do.
All that excludes the fact that this is
VERY ILLEGAL. I'm sure no one wants a trespassing charge on their record, not to mention the jail time or fine that could/would accompany it. There's a ton of great places to play that don't carry these risks.