IFMU,
It's quite different here in the UK as there are is no formal glider pilots licence. This means that gliding in this country for years has been self regulating, which has worked very well, but does leave a lot to the descretion of the club CFI. You don't
need an instructor rating to take passengers, just 50 hrs solo and the CFI's approval. However, as somebody else stated, many CFI's use the instructor rating as a yard stick. This saves a lot of hassle in sorting the good from the bad as the CFI can simply say "At this club, only instructors can take up passengers".
Interestingly it was possible up until very recently (and I think it's only the mandatory insurance that stops this now), you could own a glider, keep it at your own home strip and fly it quite legally without a licence or a certificate of airworthyness! (take passengers too I presume?) It sounds crazy, but when I looked into it a few years ago this was the case. Of course you'd have the problems of launching, but if you had a mate with a suitable tug, then you were legal
Much has changed since I flew gliders, with EASA now taking over, and the BGA loosing it's self regulatory roll. I'm not sure what the rules are now, so don't assume what I've said still applies!!!
SS