Throwing a dejada is fair and at some times, a vital skill to have. I have learned that, in singles especially, you can have success by throwing what I refer to as opposite shots with the same form. For instance, playing against players like Borja, Gallardo, Orbea, and Danny at Ft. Pierce was extremely difficult as these players could take the ball on the costado and throw down the inside or a carom with the same form. Of course this takes tremendous skill, but is extremely effective if you can do it. The most basic of this type of shot is when throwing side-arm on the right side. Just about any player has similar form throwing for the chic-chac or as a dejada. Of course, one goes to the 14 line, and the other to the 4. Being able to place the ball in two spots that far away with essentially the same form is invaluable. I know that for me, in this last season, incorporating a dejada won me a lot of points. Especially being known as someone who tries to throw the ball through the front wall, taking a big wind up and dumping the ball softly threw a lot of guys off.
So, the dejada is a necessary skill to have in jai-alai. As far as fairness, I say it is absolutely fair. The dejada is a high risk-reward shot. A well-thrown one is hard to get to, but throw it poorly and you give your opponent the ultimate advantage, effectively ending the point. It is very similar to giving your opponent the ball on the wood with a weak carom. There are a spectrum of shots available to players, including conservative throws to the back that even if thrown poorly will probably not kill you, nor win the point if thrown well. The dejada happens to be on the opposite end. I guess the one thing I could say regarding fairness is that you do not want to see a dejada early in the point. Ideally, you bury your opponent in the back or put them on a defensive rebote a few times before the door opens wide enough to throw a kill-shot. Throwing a dejada early on could be perceived as trying to get out of the point without really competing. Then again, that has its place at times too, as unexpected shots or shots from defensive positions add that surprise element. To end this, the dejada is absolutely fair and I think the game would be worse off without it.
Robertico
