Classicists aren't committed to explicit rules
The possibility of implicit rules doesn't argue against the classical symbolic framework, because there's a body of work within the classicist camp that shows how implicit rules can be modeled.
In fact, most classicists agree that at least some rules must be implicit.
However, the possibility of of explicit rule based systems does argue against connectionism, because connectionist networks can't encode such rules.
Jerry Fodor & Zenon Pylyshyn (1988)
Note: For an example of the argument (cited by Fodor & Pylyshyn) that says that explicit rules can't be encoded by connectionist networks, see "The Past-Tense Model Does Not Argue Against Rule Based Explanation" on Map 5, Box 24.