Is bad cv joint dangerous to drive?

Yes. What usually happens is the neoprene boot that covers the joint wears out and breaks. This allows contaminants to enter the joint and grease to be washed away. The CV joint's days are numbered after this happens. You have a limited amount of time to get it fixed before it fails. If it does fail, it is a safety issue. Not only will it cause severe damage to your car, but it could cause a serious accident.