Absolutely that way - the result of incompetent programming is a program "working on the desk".
Let me use your example - atomicity, e.g. a multi-byte variable X is modified both in main and interrupt.
The incompetent programmer is not aware of the problem. There is no showing-off, he simply manipulates X in the most straighforward manner.
The competent programmer knows the problem and disables/reenables interrupts upon each usage in main, except in cases where interrupt is already disabled from context.
The defensive programmer requires to use a particular routine or makro for X manipulation, where he stores the interrupt flag, disables interrupts, makes the change, restores the interrupts and returns - this allows easy future changes in the required procedure.

Jan Waclawek