I think that TnT groups get a bad rap because they're made up mostly of newbies. Any other group of riders that green would also stick out as, well, new riders who don't know how to ride very well yet. That's understandable and it's not TnT's fault.
It's good that someone is out there teaching this stuff. I do wish that they'd point instead of yelling for every obstacle though. Pointing indicates where the obstacle is, which is more important than what it is. But I'm guessing that the yelling is because not everyone is comfortable riding one-handed.
The way I look at it, its the duty of experienced riders to spot the newbies and make allowances for their inexperience.