I believe it's mostly a myth, most traders are trading lower time frames that are loaded with market noise. Lot's of whipsawing when you're on those low charts, traders just blame these market vibrations on brokers stop hunting.
Especially with regulated brokers, they are forbidden to manipulate prices, so I don't think they are going to be risking their license to stop their clients out. They've already made their spread commission when the trade was opened, whether the trader loses or profits, the broker always benefits.