Many sports have different outlooks regarding emotional displays
today, compared to years ago. Some sports had (and may still have)
strict codes of conduct. It seems, though, that in keeping with
today's generally looser morality, those codes of conduct are
not enforced the way they used to be.
Take tennis for example. Years ago, a pro tennis player wouldn't dare show disgust after losing a point, or argue a call with an umpire. Today it happens all the time, and players are not punished for it unless it's an extreme violation.
Basketball is another good example. If a player got in an NBA official's face thirty years ago, he'd get a technical foul before he could even finish what he wanted to say. Today, as long as a player doesn't swear or blatantly show up the official, he can get away with disputing the official's call.
On the Professional Bowlers Tour, players used to have to maintain professional decorum at all times. Now, emotional displays are encouraged, as long as they're not unsportsmanlike.
I, too, remember that back in 70s, jai-alai players did not let their emotions show on the court nearly as much as some of today's players do. I like to see an athlete get pumped when he does well, and express a little displeasure with himself when he screws up. It shows me that his heart is really in the game. If a pelotari makes a bad play, and he lets out a brief burst of emotion, I think that should be no problem, as long as it's not directed against anyone other than himself.
Besides, letting players express themselves a bit gives us fans a little insight into the person inside the uniform, and in my opinion that's a good thing. The popularity of a sport is normally enhanced when fans can see the players as real people.