This is my experience, too. Best method for NGC slabs. For PCGS: Bolt cutter, one cut, cutting into the "bubble" of the slab. Hinge open. Voila.
When I buy them from the coin shop slabbed I just ask them to crack them out for me not sure how he does it
I have only done this once with a NGC holder, but that's exactly how i did it. I wrapped in in a dishtowel and put it in my bench vise and it cracked open pretty easily.
What is it that you disagree with? It isn't fraudulent, as the holder is destroyed. If one were to attempt to re-insert a lesser coin back into the holder, then I would disagree with the practice. Otherwise, its my coin... "breathe the free air again, my friend!" As I said though, I personally have only done it once.
https://www.cointalk.com/threads/my-first-crack-out-thoughts.238953/page-2#post-1819253 post #22 describes my recommended slab-cracking technique.