Here some brief comments:

English is not my native language, nor do I have too many opportunities to put it to the use, so please forgive any mistakes I might commit.

You did a fine job, José Montes. Wish I could do half as well in Español.

The first thing to consider is your affirmation that us human beings have been “very lucky” not to pull a black ball out from Bostrom’s urn. What if it is not luck, but the action of forces that are unknown to us so far?

Is there any conceivable reason why a black ball cannot exist?

I do believe that many other planets in our solar system and the outer universe are inhabited by alien civilizations, but simply we are not able to perceive most of them.

That is Fermi’s question: why can’t we? The article is an attempt to speculate why we (currently) see no evidence of alien life in face of the fact that it would take any civilisation that is comparable to our own theoretically just 20 million years to colonize the entire galaxy.

Do you think all the drug dealing and drug consuming in the world is a good sign of an advanced civilization?

Clearly not good for civilisation, but also not a compelling answer to Fermi’s question. Incidentally you might be interested to read my article Dealing with drugs — what must be done.

I believe, according to my own investigations, that many alien civilizations are more advanced than us not only because they have access to better technology, but mainly because they do not have our weak characteristics, our selfishness. They have conquered themselves. Human life is not harmonious.

Once again, that is very likely the case, but it does not explain (to Fermi and me) why they are not here, swarming all over our planet, why we haven’t found the slightest trace of them in the Solar System or in all our deep sky observations. Bostrom presents one possible explanation.