Some people think that bitcoin is a scam as a result of their frequent encounters with fraudulent activities using bitcoin, and sometimes, bitcoin platforms. No matter how genuine bitcoin as a currency is, frequent encounters of scam with it or its platforms can change people's mind to consider it as a total scam without distinguishing between bitcoin and scam, but that is not appropriate. For example, for the fact that pound or dollar is a genuine currency, does not mean that scammers can not use them for scam, likewise bitcoin.
People who think or say things like that about Bitcoin or cryptocurrencies lack basic knowledge about them or the industry as a whole. Someone who studies and has knowledge about Bitcoin and cryptocurrencies, wouldn't think that way and they would know that a platform or a person using Bitcoin or cryptocurrencies to attempt a scam doesn't make that thing a scam because there can be both positive and negative use cases for anything in the world and it's the user who should be considered good or bad and not the thing.
So, such comments or statements are usually made by new users or investors that have just joined the industry and might have incurred some losses because those who has knowledge or even if they don't but have earned profits wouldn't say such things about Bitcoin and cryptocurrencies.