The implicit conversions and "we'll just randomly give you undefined to propagate ondwards" stuff is a much bigger source of bugs in JS than dynamic typing. Picky dynamically typed languages like Erlang or Python will pretty reliably produce an error/exception at the scene of the crime. (More so than C/C++!)

(Also I don't think optional static typing has gotten off the ground in Python land, or adopted in production at Dropbox?)