Yeah, to each his own is about right.
My tractor is big and old, has no cab, and the brakes are not the best. My kids are nowhere close when I am on that, especially if I am bush hogging. They know not to approach it. Period.
My daughters have been sitting on my lap on the lawn tractor since they were 2 or 3, not sure exactly but my youngest is 8 now and still rides with me sometimes. They know the rules though. They know I can't hear them so they stand out in front of my path and wave to get my attention, then they wait until it is turned off and I invite them to come closer. Once they are settled on my knee with my arm around them it will start up again. Mowing around trees and on hills means I stop it and they get off until I am finished that obstacle. Lots of nice moments on sunny days driving around together and watching the bees on the flowers and the horses in the fields.
Rules are rules and if children are taught the reason for those rules, then they will usually follow them and risk can be minimized. Nothing is ever totally safe though. My girls know that I am mostly blind when I am backing up the horse trailer, so they don't run around when that is happening. They stay in the barn and wait until I am stopped. They don't scream and fight behind a horse because a startled horse might kick. They can drive their battery powered gators all over the yard, but when I am mowing they stay clear of me because something could get thrown from the blades. They still screw up and break all of those rules now and then. That's what kids do. Then I get cranky at them. That's what parents do. Any one of those things could kill them just as easily as falling off the lawn tractor though.
Every parent sets their own acceptable level of risk when it comes to cooking/helping in the kitchen, driving in cars, riding atv's, bikes or skateboards. I expect my decisions to be different from others and am good with that. I do agree with hearing protection though. I have that covered because as soon as they are settled on my lap they proceed to grab the FM ear muffs off of my head and start rocking out to my tunes.