>I think it's more useful (and reasonable) to look at all the brutality

In what specific way is it more useful? Other than just the overall raw fact of pointing out that collective memory is often arbitrary and in flux (which I think most people intuitively accept). You certainly will not get to see people get upset or relaxed in exact proportion to the magnitude of the topics considered.

I'm asking because I've heard those arguments in various contexts and there's rarely added information other than an attempt to de-legitimize grievances through historical comparisons.

I'm not saying that this is the case here or attributing intentions to your post, but I feel it is worth mentioning the context under which these arguments might be perceived.