I have been a Sustrans supporter for many years, perhaps 15-16, by which I mean I make a small monthly contribution, used to take part in some of the inaugural rides (for fun not politicing) and avidly read all the literature etc. I'm a supporter not an activist.
My first "tour", perhaps 10 years ago was the C2C. Perhaps in the eyes of many not a real tour but I was very nervous at being away from home, out of my comfort zone and having to get from A to B on my bike with no support or get out possibilities. It was fantastic and I now tour whenever I can, which is not often enough.
Six years ago I cycled the inaugural Pennine Cycle Way ride and had great fun. It remains an excellent route. Today I'm more experienced, fitter, more confident and have a better bike. Sunday to Wednesday last week I rode the PCW from Gargrave to Berwick plus adding in a few diversions of my own, to visit Alnwick for example. On this ride I began to appreciate why some cyclists are so anti-Sustrans. Six years ago I enjoyed every moment of the route and was happy to put up with some of the sections that I now consider rather daft. Today as said I have far more experience and quickly found myself studying maps in much greater detail, rather than slavishly following the generally excellent signage, this allowed me to cut out sections which now seem a little pointless, included a rough track etc.
My point would be this. I started riding a bike about 17-18 years ago when my eldest boy wanted Dad to take him for a ride. From this I have progressed to being a cyclist, riding locally as often as possible, being a sometimes club member, confident and able to set off to average 90 miles / day with just a map, rack and small bag when I can. I got a real buzz from completing Chorley - Gargrave - Appleby via Route 68 (102 miles) in a day.
Without Sustrans, especially the C2C, I would probably not have taken up cycle touring and missed something I really enjoy. I no longer follow every mile of a Sustrans route but find they provide great ideas for tours and a reliable basis for a route which as one gains experience can be varied according to taste. For the completely inexperienced Sustrans provides the safest, in every sense of the word, option, as one grows and develops one's views develop and needs change meaning one uses the network differently.
Surely the whole point of a cycling charity is to encourage and develop cycling? Those who are dismissive of Sustrans miss the point entirely.
For the sceptics I'd strongly suggest you come and try the Lancahire Cycleway (routes 90 / 91) which makes a good 250 mile, three day tour. The route existed for many, many years and was known to cyclists, clubs etc but unless someone told you about it you wouldn't have had a clue. By signing the route Sustrans have made it accessible to all - surely a good thing? The Lancashire Cycleway has some beautiful rural riding and some blistering climbs!