[Kranar]

If you see "i++" in code and you don't have any context about what "i" is, then what difference does it make if "i" is a member variable, global variable, parameter, etc etc...

If all you see in code is a very tiny 3 character expression, you won't be able to make much of a judgement about it to begin with.

[ryao]

Not allowing a variable to implicitly refer to a member variable makes it much easier to find. If it is not declared in the function and there is no implicit dereferencing of a this pointer, the variable is global. If the variable name is commonly used and it is a member variable, it is a nightmare to hunt for the correct declaration in the codebase with cscope.