Fraud implies a wrongful or criminal deception intended to result in financial or personal gain. Coinbase not only let the people who use them know that they would not be supporting BCC, but they did so as soon as they were aware of the fork.

Coinbase had notices and a huge banner over their Overview for days that told everyone that they would not be supporting BCC and even warned about delays to support all the movement of BTC from the wallets to other places. It would be an interesting twist to accuse them of robbery or fraud of they made everyone aware of this fact well before the fork. If they had not notified anyone, and then after the 1st or later then told those who used their wallet of the fact that they were not going to support BCC then yes it would have been fraudulent and a huge fiasco.

Granted, if a person was not paying attention, had their head in the sand and did not log into Coinbase for the last week then i can see how they might feel robbed. How is this Coinbase intentionally screwing them though? I don't believe it is. I can only imagine that there are people that were ignorant enough to not monitor their investments and got caught with their hand in the cookie jar, but this is solely their fault and no one else.