As for myself, and I have been designing and fabricating electronic circuits
for over 20 years, I wouldn't attempt to interface the Inputs and Outputs of
ANY micro-controller or microprocessor directly to the outside world.  That
would violate every precaution I was ever taught plus it is just plain common
sense.  The very very minute cost of either diodes, transistors, or buffers
ICs is just not worth destroying your project.

Well, again that is my $.02 worth on the subject, nuf said by me.

Randy A.