TH was kind to send me a link to an article in El País that is worth mentioning.
Trying to display a sense of nationalism and defending stupid retaliation against Spanish people stand out in all comments I've read about this case, inflated of course by the Brazilian media. Having it as a basis of comparison, I thought the article was quite sensible, and even much more impartial than I would expect from a Spanish newspaper.
However, El País avoided going further deep into the subject and did not address problems like prostitution, illegal immigration, or what exactly are the criteria for denying the entrance - that seemed unlikely to be objective at all. One could go deeper and say their opinion about Brazilian retaliation, but that would be more appropriate for an editorial.
Definitely what should never happen in a civilized world is to treat people like dogs, like a sociologist told one of the immigration officers in Madrid. That is outrageous and unacceptable disregard. And no officer that deals with people on daily basis could be allowed to keep working if proved that he replied to the question in the title of this post saying that retained people wait for the flight back were no more than dogs ("Porque ustedes no son más que perros"). For writing about this in El País, the author of this article deserves my compliments.