Jon, sorry to hear of your experience, have to say not what I've seen at my local IAM provider Solent Advanced Motorcyclists (SAM) but no doubt it happens. I can still just remember my L plate days and certainly there were those more 'experienced' bikers who were more interested in letting me know how little I knew rather than helping me learn, human nature I'm afraid.
SAM is made up of mainly riders of larger capacity bikes but that's the same for many bike clubs, bigger/faster still seen as better but some of us have seen the light. I think SAM stipulate minimum of 250cc and capable of maintaining national speed limits, I didn't bother to take my V50 moped on any observed rides ; )