When all the terrorists, scammers and other criminals stop laundering money through the crypto currency then bitcoin will collapse. The question is when they stop doing it.
Do you even see all of the criminalities have stopped on the fiat currency? and your answer is never, they'll never stop to doing it. The criminalities will be there everytime. And it will be forever.
The dark side of the bitcoin is based on the black market and dark net which a lot of people dont know about, and that dark side is that there is a lot of money into it and the bitcoin proves to be the best way for them to hide their illegal actions, so as long as bitcoin is worthy and people use it and no one can trace you down then there always be criminal activities.