No one is saying "we're experts, accept what we say", we are trying to explain why things are done the way we are and are having to put up with smart-arses saying they know better.
You might know your car's abilities - do you know if the road surface can support your chosen safe speed? Many road surfaces are so old these days that you could quite easily go sliding off on a corner.
Then give me a warning at the corners until the time and money is available for resurfacing.
If the road surface is generally knackered then a 'slippery road' sign should be erected for a temporary period pending repairs - but then you get the CPRE complaining about too many traffic signs urbanising the countryside. And That's Terrible. The hypocracy of campaigning organisations that want lower rural speeds but no signs to encourage this (other than speed limit ones) baffles me.
Like I have said, the problem is with DfT policy - don't badger engineers who are required to follow statutory requirements, badger the DfT for making the statutory requirements in the first place.