Others seem to have tired of this discussion, but I still find it interesting.
"Is there any rule that says the symbolic name cannot be the same as the unit?"
The point is, the name and the units are different. Electromotive force is measured in volts. Current in amperes. Resistance in ohms. It violates the rules of logic and consistency to use volts, current and resistance in an equation.
For example, in mathematics there is a convention to use x, y and z for variables and a, b and c for constants. If I write an equation a = x + c, and I intend for the a to be a variable, I'll probably confuse people. Better to write y = x + c.
Same for V = IR. As Soren points out, that may confuse people. It's like babbling. Better to stick to conventions than to risk misunderstandings.
But with V = IR, the reverse may now be true. Few people use the term electromotive force anymore, so using E may be confusing. Just like no one calls "current" by its original name of "intensity."
It's an interesting issue. I don't think there is a wrong or a right. I can see grounds for both E = IR and V = IR.