I really disagree about there being a penalty for accidentally clicking a card. It's kind of like in chess where as long as you keep your hand on the piece, you can set it back down, but if you take your hand off, the move is final.
By making this a penalty, it can create a situation where you might lose a game not because of bad strategy, but because you did something out of order or clicked on the wrong card. No one wants to lose a strategy game for that reason.
And if the game is going to force the ability to be used up, then why even offer a cancel button at all?
Don't get me wrong, this developer has made an awesome and well-thought out game, but as an occasional programmer myself, I have to wonder if the reason this is intentional is more due to a concern that creating a full cancel option might open up a whole new set of bugs to deal with.