As I've said before, "at sea you run toward a fire, not away from it." The confines of a moving train would be under the same rules. The GIs knew this. "Go, Spencer!" from the inner guy kicked off the counter-attack. If nobody had "rolled" then the shooter could have just gone from seat to seat, killing everybody he saw and praising Allah all the while.
That is very true, but both at sea and in this case, training is required to negate the flight instinct, and it is duly administered, on land and at sea, and to these land-sea hybrids, the Marines. Is it not?
Other responses may also be appropriate, from people out of reach of the gunman, or lacking the strength and training to engage him. Was that the case with the Thalys employees? Did they take some passengers into a secure place and raise the alarm? If it's what they were doing, that might have been the best thing they could in practice have done. I hope we will find out.
Such a thing was done during the supermarket siege that followed the Charlie Hebdo massacre; and the person who did it was not at all denounced as a lily-livered poltroon, but was granted French citizenship in reward for his actions.
Lassana Bathily, a Malian-born and Muslim shop assistant to whom Yohan Cohen had referred as a "friend" in his personal Facebook page, has also been hailed as a hero in the hostage crisis for hiding people from the gunman and assisting police after his escape. During the hostage crisis, Bathily helped hide hostages in a cold storage container in the basement. Bathily then tried to call the police, but the line was busy, so he called his friend, a Frenchman named Dennis Mercier, and Mercier alerted the authorities ... Bathily led fifteen people into the downstairs cold storage room for safety.
Perhaps he was praising Allah all the while, for this deliverance. Who knows?