With all due respect, the most serious injuries I have ever seen on a cricket field have been Keegan Meth getting a ball smashed back at 100mph straight into his mouth while he was bowling...will they legislate that bowlers should wear helmets? If they are consistent, they would.
The absolute worst injury I have seen in cricket was Rick Darling of Australia. Rick Darling was struck by a ball by Bob Willis on the heart going for a pull shot. Darling collapsed on the pitch and nearly died but for some quick thinking of John Emburey who realised Darling had swallowed his tongue. Should all players be forced to wear chest protectors?
Cricket head gear should be a choice and it should serve a primary purpose of protecting the player, while also being appealing to wear for adults who are not obligated to wear it.
I am sure common sense will prevail.
I'd say that that incident you quote is certainly one of the worst that I've seen too. The others would include Pollard's eye, Boucher's bail to the eye, Chanderpaul being knocked out, in spite of wearing a helmet, the fifteen year old kid I saw not wearing a helmet, and the guy who's nose I broke who wasn't wearing a helmet, when I was a teenager. I've seen enough ambulances relating to head injuries and cricket and accompanied many people to hospital, and tend to think that helmets are a good idea.
I don't think anyone is mandating that an adult should be made to wear a helmet, or any other protection, although, in certain circumstances, you'd be pretty dumb not to if it was available (would you deliberately walk out without a box? Some do!).
As you say - common sense will prevail.