Those people claiming bitcoin is scam, they are noobs on crypto currency trying to be on hyped train just wanted to fit in and make venture with but they don't really know what bitcoin is. They are just crybabies and weak hand holders wanted to make profit fast and easy but hey that's not how bitcoin works or any crypto currencies at all.
I think those people are afraid to use bitcoin, or some people try to discourage the others about bitcoin. Bitcoin is not a scam, people it's self is scam who use bitcoin in thier illegal activities.