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I can think of at least 1 country without external debt (Brunei) that has been very worried about its economy for the past few years since oil price dropped. Had they borrowed money -- and invested their income from oil in sovereign funds for example, instead of lavishing their reserves -- to develop and diversify their economy, they might not be in their problem today with stagnating industries and unemployment.
I agree with you. Borrowing money for further development is an integral part of the modern economy. Since there is no better economic model around yet, judging about the economic situation in a country by the size of its debt is a fallacy. If only the countries with much smaller debt were prospering, but this obviously not the case.