I'll always go on a ride, even if I'm afraid. It has happened on Oblivion, Detonator and The Freezer at previous CF-Lives, I just rant about how I'm afraid, and then I throw up hands in the air and get on with it. I'd never leave the queue line, I'd just try and ride my fear away. For me it's certainly not a case of "if you don't like it, don't do it again", it's a case of "if you don't like it, just shut up and ride it anyways". The only time I wouldn't go on a ride is if I was about to be sick. I don't think fear could prevent me from riding, only because I'd seriously regret it afterwards.
I've never ever left a ride after I've joined the q line let alone getting on the ride, if I'm in the q then I'm gonna ride, never been any different as of now and I dont intend on changing that, fear all adds up to make it even more thrilling I think. Just get on with it and do it I say, leaving from the q is fair enough but waiting till your on the ride to change your mind is pushing it, if you've been man enough to q for all that time then just get on with it and ride the bl**dy thing!
I have this view from one of my visits to BPB, was on Ice Blast, young woman next to me was rather terrified about the whole idea, the ride op come round to do the usual check on the restraints and she asked to be let off the ride, his reply was, "ahh you'll be fine" then walked away, she turned to me looking rather worried asking me lots of things about the ride, after a bit of reassurance from me she calmed down, after the ride was over the 1st thing she said to me was how amazing it was and she wanted to do it again. My point being that 99% of the time no matter how scared people are to begin with they always end up having a great time!