I totally agree with you mcem. I never resort to incorrect forms just because they are in common usage. I am quite happy to accept that language evolves, that the meaning of words can change, sometimes dramatically, but I refuse to be party to something that is incorrect at the moment.
If the evolution of our language results, at some future time, in "Me am going to the zoo" (or "Me is going to the zoo") being the correct form then I'll happily go along with it (though I doubt I'll still be around
). In the meantime it is "I am going to the zoo" and, therefore, "Rosie and I are going to the zoo". Nothing will budge me from this.
English grammar was taught properly when I was at school and these rules were drummed into me, both at school and at home.