Personally I would not use a harness on a rabbit either. I would be afraid they would hurt themselves or that it would freak them out. It's not so much the person with the leash would pull but rather the animal would pull. Dogs choke themselves all the time when they get over excited and pull on a leash. I worry about the safety of the rabbit if it suddenly tried to escape or hop out of range of the leash. Also I don't think harnesses are properly sized for most rabbits and definitely not chinchillas (assuming it was safe to use one with a chin at all, which it's not) and I'd be concerned it would be too tight/too loose and the animal would escape. I think playpens and rooms made safe are a better option. Where would you walk a rabbit anyway? Outside it would be exposed to all sorts of new illnesses as well as fleas, etc. Definitely it'd be much safer than taking a chinchilla out the same way. As you said I'd never even consider putting a chin on a harness. I honestly think a 'death ball' would be safer for a chin than a harness.
Personally, I think rabbits really benefit from outdoor time, but I also live in Calgary where we don't have fleas and such, so it is different. And if you know the harness to use and how to fit it, you don't really need to be overly concerned unless you don't know your rabbit or it's an easily frightened animal. It doesn come down to the individual animal.
HOWEVER, a lot of people, myself included, find a lot of rabbits really enjoy being outside and I would almost think it crueler to keep them inside all the time. Being in grass you know is safe is great stimulation for the rabbit, foraging and digging and lying in the sun and frolicking until their hearts content. I see how my rabbits (And I have 12 rescues, as well as some fosters, so there is variety in my rabbits personalities) love being outside. And when they are used to the harness, it is an easier way of keeping control over the situation.
I really think people completely underestimate how social and curious rabbits are. Most are more curious about things then afraid, and they aren't as likely to bolt as everyone thinks they are (But like I said, individual personalities) and mine enjoy going on walks.
But it comes down to how much you trust your bunny. If you don't trust your rabbit, you're not going to be comfortable.
But still, off topic. A chin should never be in a harness OR a ball.