If you end up in a situation where you need to bring your passengers attention to the fact that what they want you to do isn't safe, ask them to ring their insurance company and have your wife/partner/boyfriend/casual root/mother/father/bloke next door the beneficiery of their life policy.
You want to make it worth your while to die for someone you're not sleeping with!
I'd rather be alive looking for a job than dead and not needing one. I've worked long and bloody hard to get to where I am now (one rung off the bottom of the ladder). And NO ONE can afford to pay me emough to take unacceptable risk.
And yes, I have said "no" on a number of accasions, both on EMS and corporate tasks