I tend to agree with you. We don't really know exactly what transpired in most of that conversation, but I'd imagine Giles had past situations running through his memory, and was going to see to it that the horrible results didn't happen this time. From his standpoint, he was probably seeing a situation in which, yet again, someone was wanting to use black arts to bring back a loved one who was simply already gone. And let's not forget that he's got darn good reason not to trust Angel, in the first place.