All too often, people use the Define Projection tool when they really want to use the Project tool, thinking that if they use it, their data will be projected into the coordinate system that they want.
I suggest that the Define Projection tool
- be renamed to Initial Projection or Fix Projection something similar OR
- checks to prevent projected data being defined as geographic should be implemented and persistent in the interface
- Also, this tool should, or could be disabled, if a coordinate system already exists, allowing the user time to think about what they are really trying to do.
The two proposals Initial and Fix projection could call the same code essentially, allowing one to define a coordinate system for which one doesn't exist or to fix one that is incorrect.