Not all "deniers" were crackpots, at least back then.
And in all fairness, some of the science that led to the discovery of HIV was a bit dodgy, in terms of how it was executed and reported (not, in hindsight, with regard to its contents). Also, the proposed mechanisms of how HIV works were rather novel for the time, so it is not hard to see why some more conservative members of the science community might have been on the fence for a while about whether this was indeed the cause of AIDS. Add to this that even someone like Kary Mullis, who got his Nobel Prize for PCR, a fairly pivotal molecular biology technology, were skeptical, at least for a time.
Of course, nowadays, we know enormously more about the molecular mechanics of HIV and AIDS than we did back then. So by contemporary standards, even the "deniers" from back then who tried to be skeptical on actual scientific grounds look like idiots. And some of them likely were - but not all of them. Not judging from the perspective of the time they were living in.