I give the "ride within limits, be an adult" speech to all my racers because that's the truth. I don't know everyone's skill/comfort level. I find that by trusting folks is more effective than trying to scare them.
As a race promoter, I can control certain things....EMT, safety plan, helmet rule, waivers, liability insurance, the trails we build/race. I can't control some dummy trying to do his best Sam Hill impression. So I don't try....
Also, FREE BARTMAN!!!