The issue with helmets is that you need to know what you are trying to protect against. If you don't make that assessment first, you're just w**king. Helmets for race cars are different from motorbikes are different from cyclists are different from equestrian.
Wearing of parachutes is not required in Australia and very few aerobatic pilots wear them, so unless you are one of this minority, there is no requirement for bail out protection.
One of the reasons helmets are worn in car racing is because of the potential of debris inside the cabin hitting you on the head, or hitting your head against the roll cage. Neither of these conditions exist in an aeroplane and frankly, in an aerobatic aircraft if you hit the ground with any real force its lack of crashworthiness may mean the hitting your head on the canopy is the least of your worries.
The arguments against helmets are increased weight on your neck under "g" and reduced peripheral vision.
One of the advantages of aviation is that very good data is kept on accidents. So we don't need to shadow box at potential risks, we can consider the pattern of history. None of the people I know who have been injured or killed in aerobatic aircraft would have benefited one iota from a helmet. In fact I can't recall any that would have benefited from a parachute. Although I had an animated dinner one night with Kermit Weeks who reeled of a list of people he knew who had been saved by parachutes.