Comment by somenameforme

51% attacks, on anything at a large scale, are generally more theoretic than practical. The amount of resources you'd need to invest to achieve that on any large currency are astronomical, and you'd need to just completely wreck everything engaging in widescale fraud (which would be a felony, carried out repeatedly and at scale - and likely fairly easy to tie back to you given the massive resource investment to get here in the first place) to try to recoup your losses.

The most probable outcome being a rapid fork and rollback as already with e.g. Ethereum over a relatively negligible amount of money relative to what you'd need to get a 51% on Bitcoin. You'd likely end up losing a massive amount of money, as well as look at possibly spending the rest of your life in prison. So the only real purpose in doing so is for attention or trolling, but the costs involved generally preclude this motivation.