As with all walks of life, you're always going to find some people that are an issue.
From personal experience, I've found most people respectful of footpaths and rights of way. On one farm we had a footpath that went right through the yard and down through the field to woods. There was always an awareness for us because of machinery and livestock, but it wasn't as though there was a constant flow of people and as I mentioned, people were respectful.
On another farm we actually cut the brambles encroaching the footpaths to keep the access clear. Our serious issue there was with dogs from time to time. I'm not sure if anybody has seen the aftermath of dogs mauling sheep, but I can assure you, it's not a pleasant sight and one I have never forgotten.
These may be open fields making up a beautiful countryside, but it's also a business and the livelihood for thousands of families. The vast majority of farmers would have no issue with people walking, as long as they didn't litter, CLOSED FUCKIN' GATES, kept dogs under control and didn't damage crops. It's just basic respect, nothing more.
I don't know the details of the examples mentioned, but I'd suggest if the actual facts were known, some would of course be bloody mindedness, but probably more to do with the farmers fed up with damage, littering and gates.
All this bollocks like, "Landowning rich fucks deny us access because they want the feudal system to continue" or "these cunts still lord it over us and continue to suck us dry." are living in some sort of envious/jealousy/insecurity ridden world. Sure there are very some wealthy inherited landowners, but the vast majority of farmers are just working hard trying to make a living in an industry where it's becoming harder and harder to do so.
I wouldn't be in favour of a broad right to roam, especially across working farmland, but I'm sure there could be many areas suitable to be opened up for walking.