To be sure, we are no strangers to tragedy and death. But in general such things are due to an outside cause - terrorism, persecution, famine, and so on. These deaths occurred simply in the context of a religious celebration. It's just heart-wrenching.
Originally I wasn't going to write anything other than expressing grief, and wishes for the recovery of the injured. But then I saw some people on Twitter criticizing those who went, on purportedly rationalist grounds. They argued that mass gatherings of this sort are darkei Emori, and they pointed out how Rambam was opposed to visiting the graves of the righteous, and proclaimed that the righteous are memorialized through their teachings, not through pilgrimages to their graves.
Aside from being deeply insensitive, such critiques are wrong for other reasons. I personally am not interested in attending the Lag B'Omer celebrations at Meron. But the Meron celebrations are certainly a tremendous source of religious inspiration for many people. And one should not attempt to delegitimize those who follow the mystical approach. If people are inspired by the Meron celebrations, that is a wonderful, positive thing.
It's also important not apportion any blame to the people who went, even unintentionally. Even describing it as a "stampede" is wrong. Consider this frightening but important discussion from Wikipedia:
Academic experts who study crowd movements and crushing disasters oppose the use of the term "stampede".[9] "The rhetoric of 'stampede' is often used to imply that the crowd is animalistic or mindless". Most reported "stampedes" are better understood as "progressive crowd collapses":[9][10] beginning at densities of about six[9] or seven[8] people per square meter, individuals are pressed so closely against each other they are unable to move as individuals, and shockwaves can travel through a crowd which, at such densities, behaves somewhat like a fluid.[8] If a single person falls, or other people reach down to help, waves of bodies can be involuntarily precipitated forward into the open space.[9] One such shockwave can create other openings in the crowd nearby, precipitating further crushing.[9] Unable to draw breath, individuals in a crowd can also be crushed while standing.[8] Journalistic misuse of the term "stampede", says Edwin Galea of the University of Greenwich, is the result of "pure ignorance and laziness ... it gives the impression that it was a mindless crowd only caring about themselves, and they were prepared to crush people."[9] In reality, individuals are directly crushed by others nearby who have no choice, and those who can choose are too distant from the epicenter to be aware of what is happening.[9] Among causes of fatal crushes, sometimes described as "crazes", is when a large crowd is trying to get toward something; typically occurring when members at the back of a large crowd continue pushing forward not knowing that those at the front are being crushed, or because of something that forces them to move.[11]
There are crucial lessons to be taken from this terrible tragedy. But not a critique of the people who went. And the lessons should wait for another day.