I am confused by other this word is being used nowadays. Many define as scam what they dislike, very often as an overreaction and to attract attention. But words have meanings, languages have depth and a rich vocabulary. Let's be precise and not call dishonest what we disagree on.
Quick references for everyone with definitions of the word "scam" by world famous dictionaries:
An illegal plan for making money, especially one that involves tricking people.
A dishonest scheme; a fraud.
A fraudulent scheme performed by a dishonest individual, group, or company in an attempt obtain money or something else of value. Scams traditionally resided in confidence tricks, where an individual would misrepresent themselves as someone with skill or authority, i.e. a doctor, lawyer, investor. After the internet became widely used, new forms of scams emerged such as lottery scams, scam baiting, email spoofing, phishing, or request for helps. These are considered to be email fraud. Also see phishing, scheme
A scam is an illegal trick, usually with the purpose of getting money from people or avoiding paying tax.
Behind all these definition, there is the notion of hiding the intention of the service offered, to "trick" someone, like a magician would do, keeping your attention away of his real actions.
Applied to cry currencies, assets and ICO, we have to think about the activities or features that are sold to the investors and the facts that proves that they are indeed real. Let's also be cautious: it's not because we have difficulty to find the proofs that the coin/token is automatically "a scam". Let's not be short sighted but rationale.
I am someone who prefer to keep a skeptical approach to things, as I am a very risk adverse person. Nonetheless, I don't scream "scam" to everything I disagree on or don't understand. When I find empty promises, I use it.
Is Bitcoin a scam? No.
Is Bitcoin cash a scam? No.
Is Ethereum a scam? No.
Are alt coins in general scams? No, not by default! I think it's in general difficult to be fraudulent when some keys of a public blockchains are given to users and minors. But I may be proven wrong!
But...
Is Ripple a scam? Yes. (I wrote an article about why: https://steemit.com/ripple/@pada-1/my-thought-about-ripple-xrp)
Was Bitconnect a scam? Yes.