Contact with Alien Civilizations

I just read a long and serious, but unfortunately rather tedious and repetitive book by Michael A. G. Michaud: Contact with Alien Civilizations: Our Hopes and Fears about Encountering Extraterrestrials.

Many people, otherwise very intelligent and with broad philosophical perspectives on the world, life, and nature, are unreasonably, even irrationally, dismissive of this entire subject. This book, unfortunately, however, although it purports to go beyond the usual discussion of SETI (the search aspect), to discuss the likely implications of either communication or direct contact with intelligent aliens, really adds nothing new to the conversation.

The fact is that in all the evidence of the long history of life on Earth there's no proof  (at least that we've found so far) that anything was left behind that credibly indicates visitation by technological intelligent aliens to our planet at any time in the past. Also, despite some looking, we haven't found any evidence of alien technologies "out there" (either in the form of signals or indirect evidence, such as unusual radiation signatures from astronomical objects indicating technological origin). The search for any of these types of evidence (or for artifacts in the solar system other than on Earth), has been far from exhaustive. I think the case for spending at least some modest resources on all of these is pretty solid, but until there is unequivocal proof that humans are not effectively alone in this part of the universe (because if intelligent aliens are too far away, they effectively don't exist, for us), this subject just runs out of steam. It remains an endeavor of knowledge that lacks proof of the existence of its subject matter.