(ETA: Ooops, I think I came across a bit harshly in this? Your thoughts on this topic are very inspiring! You do well in pointing out that the "a product of their time" argument is usually apologistic --- my approach in instances like this is usually to search for a way to break out of the confines that arguments like the one you're criticizing present.)

I think the inherent problem of the "product of their time" argument lies in its implied judgment of a person, and furthermore the idea that a person's actions as a whole can be integrated into what we perceive as their character. So what if it is hard to evaluate the moral standards a person shows in their actions - we can still talk about and evaluate the actions themselves - and yes, compare them to the actions contemporary people took. I totally understand (and share) the impulse to think about people in terms of good or bad (or progressive, or reactionary, whatever), but I feel that when it comes to problematic aspects, talking about concrete actions instead of trying to integrate them into our preconceived notion of what a "good" person is supposed to be like makes true discussion possible (or at least more feasible).