Highbeam, I absolutely agree and use my parking break all the time. The safety issue comes when you're using the tractor and it doesn't stop as you would expect. That alone is an issue, but so is an over compensating when you hit reverse too hard to stop it. Mine got so bad it became difficult to control properly and would continue as if your foot was to the floor for 20-30 feet before it would even think about slowing down. I'm betting it would have continued creeping 600 ft + before stopping altogether, if it ever did.
Being aware of the issue means it's probably not going to lead to an accident, but with other people using the tractor or using the tractor with kids around, I wasn't willing to take even the slightest risk. Being covered by warranty probably helped my resolve and I'm not sure what I would have done if my dealer told me I had to pay $3000 fix the problem and it wasn't covered.