Cracking it is not bad. People say that cracking your knuckles causes arthritis but that's a myth. Cracking your fingers or necks releases gas from between your bones. That's the sound you hear when you do it
It could be very dangerous if someone else, someone who isn't a chiropractor cracks your neck for you. Someone who doesn't know what they're doing could very easily, and accidentally break your neck. Cracking it yourself...? I'm sure nothing terrible will happen to you. Been cracking mine from time-to-time all my life & nothing "bad" has happened to my neck. :)
Only if you can put 60 pounds of torque behind it when you crack it. Aside from that, it is perfectly fine and natural, if cracking the air pockets in your bones was actually bad, chiropractors wouldn't have jobs.