A lot has been said already but I’ll add a bit.
My mates and I have been cycling up/down/around Corstorphine Hill (Corry H, Clerry H) for well over 15 years. A blast up the Hill is one of the best ways to fill a summer evening, without doubt. I used to live in Drum Brae about 2 mins away, but I now live about a 15 min cycle; however, I’ll still be heading up regularly.
You can happily spend an hour there without covering the same bit of trail twice and there are some superb natural drops, jumps, descents and climbs. Lots of nice wee sections of trail which have appeared over the years. My favourite blast is down to Corstorphine Road along the fence of the Zoo. Nice single track at the top past the wall and you can really motor over the grass clearings and take some pretty big air over the fire site. It really is a gem in West Edinburgh. Which other city in the UK lets you mountain bike past a herd of Zebras?!
Back to the OP – there is absolutely nothing wrong with cycling on the Hill. The ‘Friends of Corstorphine Hill’ are ill-informed and petty. The way they block the trails actually causes more harm to the environment than if they just left everyone to their own devices. I do worry sometimes that some of the kids might not be the most considerate but sensible adults should not cause any hard feelings with the walkers.
IMBA – interesting that you are getting involved, I’ve always thought that Corstorphine Hill’s trails, if formalised, could make a superb mini-trail centre, although I’m pretty sure there aren’t enough to be for the exclusive use of anyone in particular. I guess they’d have to be shared but they could be way-marked, I suppose. It will certainly give the considerable number of MTBers a voice.