I can assure you that their concerns are heartfelt and in a lot of cases quite valid.
People feel that bikers are intimidatingly fast - bikers need to slow down completely, as in right down to walking pace plus walking pace, when they get anywhere near walkers. Or just stop. Your perception of speed on a bike is totally different to a family strolling with kids and dog.
People also feel that bikers are arrogant and are not sharing their experience of the countryside - they think we are on an adrenaline ride and not tuned into the outdoors in a wider sense.
Also there are conservation issues beyond just simple erosion. Ground nesting birds and lizards for example. A lot of creatures need an extended patch to feel comfortable and thrive, not just ever decreasing isolated patches hedged by a maze of mtb tracks.
Plus there are genuine health and safety issues. Liability is a worry for land owners, but also a general concern that most people don't want serious injuries happening regardless of blame or litigation. The poor guy that broke his neck for example - that situation is not suddenly ok just because no law suit was pursued - he still broke his neck.
The Ranger will leave "legacy" trails - but you might have a different list in mind to him!
More visitors is generally a good thing. It helps the local economy (we aren't a theme park here - it is a real place with people earning a living and bringing up families etc) and that is one reason that bodies such as Surrey Hills AONB are behind cycling. But there has to be some harmony and tuning-in.