To the OP, it's not vandalism, but is pretty irritating in places. I'd prefer there was no need for pitching because people considered the results of their actions when out and about. If I want to ride stairs I can always go to the nearest tower block or multi-storey fire escape. Unfortunately (as yet) I'm yet to find one of those that has steep twisty singletrack instead of steps.
Whilst the link that elliptic provided (above) is pretty basic and aimed at walkers, it points out that there's little else other than pitching that can be done to stabilise the surface on such heavily used and steep slopes. Nobody wants pitching – it's a pain to run or walk on (can be fun to ride down though if done well), costs a fortune, and takes a lot of effort. That said, if it is there, use it. If you don't, all you're doing is encouraging erosion elsewhere.
Basically, if you don't want to ride on (badly) maintained trails, use them in such a way as the maintenance is unnecessary in the first place. If that means riding through puddles rather than round them, getting off for the odd drainage ditch you don't like the look of, or in bad conditions choosing a route where your impact is lessened, so be it. If you feel you can improve how track maintenance is done in the future, then get involved- a lot of the work is done by volunteers.
Arguments on here along the lines of “i ride where I like 'cos the steps are no fun, erosion is natural anyway, and anyway I heard a ranger say not to ride on the path anyway so nur-nur-ne-nur-nuh [paraphrasing slightly] are disingenuous to the point of absurdity.