1) The "cum hoc, ergo propter hoc" nature of the central argument for infrastructure. (As remarked previously, I think, the Dutch began with a higher level of cycling, and have been spending without a huge increase (although still one that would make many here envious, and there are cultural differences too)
It was without any increase at all so hardly something to be envious about.
2) The fact that British designed and built infrastructure is generally poor, badly maintained, rarely linked - and because of that there's a huge lack of belief in it as an end[1]. (And the argument that the new stuff will be "good quality" generally comes across as special pleading, if not what we've heard from our councils for years)
An antipathy towards infrastructure is often described as "bias", when, if you've ridden any of it in the UK, it's a perfectly defensible, evidence and experience based position to hold. The leap of faith here surely comes from the segregationists, who want us to believe that the same councils, highways engineers &c cresponsible for the largely dire stuff we have now can produce something that isn't at best useless, or at worst dangerous.
A classic is Byng Place on the segregated cycle facility in London - a flagship facility for the fans of segregation. There were a number of accidents and near misses from cars turning across the cycle track. As a result the Council decided the solution was to put give way signs for cyclists on the cycle track either side of the junction. So now any accidents are no longer the fault of the driver but are the cyclist's.