The more options are left open for runtime bugs, the more bugs will be in the final product.
Maybe if all else were equal, but it's not. I could argue that the time you save with a dynamic language leaves more time for debugging, and that the kinds of errors a type system helps with are generally the kind that show up early and are easy to fix.
Anyway, there's a reason I asked for evidence and not arguments. I've heard plenty of the latter already.
The more options there are for converting one value to another, the more bugs there will be in the final product. There is a lot of things that can go wrong during conversion.
I'm not sure how this is relevant to dynamic typing. Are you referring to weak typing?