Anyway, without getting into it in too much depth, my reasons for citing it (the Irish famine) stem from: 1 million dead (reasonably rigorous estimates by proper statistical types) when there was more than enough food being produced to feed everyone, but a lot of it was being exported. I do agree that it is debateable as to causes and culpability, but I'm calling genocide on the basis of the result.
But just in terms of culpability (and this applies to other ones, including that 1940s german thing), to what extent does culpability extend not just to those who perpetrate, but also to those who could have intervened, but stood by and allowed the horror?
Similarly the genocides perpetrated against native peoples of North America and Australia tend to get short shrift in UK school curricula. Teaching about these seem to be associated (as does Irish Famine) with a "political" viewpoint, in a way that the Holocaust doesn't.