I agree that using terms like "good" and "evil" only serves to muddy the water. I prefer the Vodou lingo of "hot" and "cool" spirits. By that definition, Goetic entities are definitely hot. They are fast-acting, strong and close to the material plane: they can also be difficult to handle and have a tendency to turn on the summoner if they sense weakness. There are plenty of djabs which behave in this fashion, and plenty of practitioners who are able to work successfully with those djabs.
In my experience I have found that Goetic entities are, for lack of a better word, corrosive. If the proper shields and protections are not in place, the magician can experience negative effects. From an alt.magick post I made in March 1995:
In January of 1991 I had a Goetic working backfire on me. I had worked with this particular entity (Furcas, aka Forcas) before and had always had positive results. This time I summoned him with a somewhat more negative intention: to cause grievous bodily injury to a person who had ripped me off for a substantial sum of money.(I should note that I now see the Goetic entities as indepenent and sentient entities, not constructs. Other than that, this post remains a pretty accurate description of my experience with Furcas).
No, I wasn't found with one toe outside my "Ritual Circle" and my head twisted 180 degrees. And yes, I did get some results. The person who ripped me off had several ribs broken in a gang attack, lost his girlfriend, and went from being a promising musician to having all his guitar equipment stolen.
What happened was the Furcas energy or entity "bled over" from magickal space (i.e. the ritual) and started obsessing my personality. (I see the Goetic demons as constructs within the collective unconscious; others may disagree with me). Several very close friends refused to have anything to do with me, as they said I had become "hard" and "mean." (I found stuff like Faces of Death unutterably funny, for example). I became fascinated with Richard Ramirez to the point where I stuck up a picture of him in my apartment (the one where he's holding up the pentagram drawn on his hand). I also remember a profound feeling of disassociation. There were times when I would look into a mirror and not recognize the person looking back.
In a couple months this went away. To this day I still haven't regained some of the friends I lost, though (not that it matters at this point) and still feel like there's emotional "scar tissue" in certain points of my psyche. Not as spectacular as a dragon summoning killing a dozen people, true... but that's the best I have to offer.
My personal feeling is that Goetic entities (I'm deliberately avoiding calling them "demons" because I realize that is a loaded term that contains a lot of Christian baggage) are not just non-human but non-mammalian. David Cronenberg's line about "insect politics" comes to mind. They are not capable of mammalian emotions like bonding and nurturing: they aren't going to become our friends and they see attempts to negotiate as signs of weakness. The only language they understand is power: the only way to deal with them is to force them to do your bidding. And once you've done this you had best watch your back, since they have long memories.
Others may have had a different experience than mine and may have established a different relationship with the Goetic entities. All I am going by is what I have seen and felt. As I said in the original review of Jason's book, we can agree to disagree. When it comes to magic, there are no experts: there are only those who have come to the Temple by their own path.