Ethereum Gas – Potential Abuse of Free view or pure Functions

Calling a constant function inside a transaction costs just as much as calling a non-constant function inside a transaction. What constant means is that since it doesn't alter the state, your local node can run it and tell you the result without needing a transaction. This doesn't cost gas because only your node has to run the calculation.

You may be able to use this to save gas in a transaction by first running the constant function from your JavaScript code to get a result, then passing that result as a parameter to the transaction. However, unless your contract trusts the person sending it, you still need to verify it inside the transaction. This may still be useful: If you have a sorted list and you want to know where to put an item, it may be useful to check it on the client side and find the index x, pass in the index x as a transaction parameter, then let the smart contract code in the transaction verify that the item at x-1 comes before what you're adding, and the item at x+1 comes after it.

One pitfall is that the data may change between reading a result and sending a call containing it to the blockchain in a transaction, in which case your transaction will fail and you will have to send it again.

Yes, pure/view functions are bound to the same gas constraints than transactions. They need gas to be executed. The only difference is that the gas is not paid for.