When I saw who the post was from I knew you wouldn't mince words or Sugar coat your opinions!!
To the orginal poster - I agree that this sounds dangerous. Especially if it done with any regularity and certainly if it is done for as long as half an hour! Pain is your body's way of telling you to stop this.
Do you want your vagina all stretched out for your future? Fisting would become your only way of feeling vaginal stimulation if you keep this up. If you tried fisting because your vaginal muscles are already loose, this will only make it worse. Try doing exercises to tighten that baby up. Stop taking p 0 r n so seriously that you have to try everything you see.