Too Fast,
is not a question of agreeing. The legal system in Spain is fundamentaly different to the legal system in anglosaxon countries. There are many legal principles that do not translate easily between the two systems. Airline captains clearly do not chase criminals however their instructions must be followed by law. The Spanish legal system did not contemplate giving such power to non nationals in the same way that you must be a spanish national to be a policeman, judge, MP, army officer, etc. If this principle does not apply in your country then great, that is what makes the world an interesting place we are all different. A little cultural perspective might not go amiss. Your system isn't always the only system nor the best system. This law came from well before airplanes and there is a certain logic to it if you care to look for it.