Which is it - zealous or over zealous? I don't like either.
No point getting their backs up by harassing them.
Two comments (so far) to their website pointing out that they are in error hardly constitutes 'harassment'. Assuming you'd seen their website and its seeming 'OK' to climb Silbury, "...for a view around the country side" how would you have responded? (assuming that you don't think it's alright to climb protected monuments).