My 2 cents.
I've been riding and racing professionally for over 20 years. Always wear a helmet as well as my kids - bikes, quads, dirtbikes, doesn't matter.
I was t-boned by a dopey kid trail riding in 2002, he was passing his buddy on a two way trail, 5 gear tapped on his KX250. He hit my NEW 400EX so hard when his front tire pushed passed my nerf bars it ripped his forks off. Having raced for many years I had full gear on so I managed with just some extreme soreness and a totaled quad. Actually cracked my engine case where the pivot shaft goes thru the engine and frame. (anyone wondering it was the trail system in Black River Falls, WI)
A good friend of mine was tooling around on his TRX300EX, 1st gear no helmet in the yard. Tie rod bent for no apparent reason but sent him over the bars and the quad following. Luckly no damage but could have been worse.
Do as you will but remember ATV's aren't safe from legislation just as hunting isn't. There are plenty of groups out there trying to ban them and sue the pants off the manufacturers based on the fact people can get hurt. We just had a ban come thru on small displacement machines because of lead paint on the frame. I don't know about you but I don't let my kid chew on his footpegs.....
Do or do not, there is no try - Yoda