I agree. If it doesn't feel right, don't do it.
Peer pressure, either direct (as in "aww c'mon, don't bail, you big wuss!) or indirect (as in, "these guys will think I'm a big wuss if I bail, and the hot diver chick will never look at me again"), is a killer - or at the very least a killer of enjoyment for everybody involved.
Sometimes this can be eliminated, however (to a point) by discussing the dive thoroughly beforehand. Consider two extreme examples:
Situation 1:
Nervous diver: "Hey guys, I'm really nervous about this, I've never done it before, what's the deal?"
Reply: "Don't worry, the reef is six metres deep, the vis is forever, there's zero current, I've been here 500 times with my buddy, and we've got all the latest lights and bells and whistles and emergency equipment, and we've got these standard procedures to follow so if you find yourself alone, just wait at the surface with your illuminated SMB and we'll be with you in a matter of minutes, we can always come back tomorrow, try it, you might like it, we'll look after you"
Hot Diver Chick: "Hey, if you're nervous, I'll hold your hand for the whole dive if you promise to take me out for dinner later"
No Longer Nervous Diver: "okay I'm sold, let's go"
Situation 2:
Nervous diver: "Hey guys, I'm not sure about this dive"
Reply: "You big wuss, call yourself a diver? Live it on the edge man, that's what diving's all about!"
Hot Diver Chick: "Are you getting dressed or not? I'm not waiting around. It's a killer site, bring it, or get out of my face!"
Previously Nervous, Now Panicking Diver: "EEEEEEK!"
Okay, I joke, but as a guide, I see this all the time. Some of that worry can be very easily eliminated by a thorough discussion of the dive site, the plan, potential hazards, knowing that the rest of the team will be giving you extra special attention during the dive; safe, thoughtful diving. If at the end of that discussion, the diver is still not comfortable then no worries. Keep the soup hot or the beer cold, and we'll see you in the pub later.
But if a diver isn't "feeling it", knows in their gut that this dive is not for them, and then is big enough to stand up and own up to their own limitations and call the dive? Well, that's *exactly* the kind of diver I want to go diving with.
Cheers
C.