Yes, it can be dangerous. Any movement in it, and the particles will become airbone, and will be in the air you breathe. However, if it is left undisturbed, it wont release particles, and wont be dangerous. Not a good situation, since there is always a chance that someone will have to go into the attic for something. If you remove it, it has to be professionally removed.

As long as you don't disturb it there is no problem. Even then you have to expose yourself over a long period of time (occupation exposure) to get asbestosis. Every house built before 1978 likely has lead and asbestos somewhere.

If it is old vermiculite, yes, it probably contains some asbestos and the above comments suffice. I have purchased vermiculite (~2006-ish) that stated on the bag that it came from a non-asbestos source, FWTW.

EPA tested vermiculite insulation years ago and found that the products from some manufacturers were asbestos-free and from others not. You can only tell by having a sample tested. I had a couple of inches of vermiculite in the attic of a 1952 vintage home and I had about 4" of blown-in insulation added on top of the vermiculite. I don't know if my vermiculite contained asbestos or not, but I never worried about it after it was covered by the additional insulation.

1) test it for asbestos. If it comes back negative you have no problem

2) consider how much time you spend in the attic disturbing the insulation. If it's not much you have no problem

3) if you have massive air infiltration that would carry dust and particles into your house you have a different problem, and need to seal all those openings anyway.