What evidence is there that $coRP \neq NP$?
When considering the power of non-determinism (P vs NP), randomization seems like a 2nd order issue.  In particular when we think about "P=NP?" we are really interested in the question "are all NP problems tractable", where randomization could be allowed, so tractability really means "in BPP".  So "NP contained in BPP" seems essentially as unlikely as "P=NP", and in fact if these were considered different then people would care about the former rather than the latter.  (The peculiar variant "NP in coRP" is formally somewhere in the middle between these two, but conceptually essentially the same).    If good enough pseudo random generators exist then the two questions are formally the same.  Similarly, in "non-uniform settings" randomization is known not to help and thus "NP in BPP" implies that NP has poly-size circuits.