Asimov was not in the "try to come with a good framework for robot ethics" business. He was in the business of trying to come up with some simple, intuitive idea that didn't require the readers to have a degree in ethics and that was broken and vague enough to have a plenty of counterexamples to make stories about.

In short, Asimov absolutely did not propose his framework as an actually workable one, any more than, say, Atwood proposed the Gilead as a workable framework for society. They were nothing but story premises that the consequences of which the respective authors wanted to explore.