Do modifier keys (control, alt, command, fn, shift) fall under your definition of modal UI? If so, how do you deal with the fact that your keyboard doesn't (I'm guessing) have dedicated keys for cut, copy, and paste? I think its safe to assume that everybody uses those significantly more often than they step through a program with a debugger.
Then you lose the ability to change the code while you're debugging it, or end up with a modal UI. No thanks.