@Thomas,
It's not a problem . . . it's a matter of there being a valid distinction. The Iceni slaughtered Romanized Britons because they had "Romanized," and they slaughtered Romans because they were Romans. But they weren't doing it systematically, as a part of an organized program of an established, functioning government. The Romans who then slaughtered the Iceni did it as a function of long-established state policy, but not necessarily because they were Iceni. Members of the Iceni tribe who stayed home were not hunted down to be killed. But the scale was only horrendous in proportion to the population of Britannia. As a function of the overall population of Europe, it was not a very notable slaughter.
The Franks slaughtered Saxons because they were "pagan," not because they were Saxons. The Saxons slaughtered Franks in return as an act of revenge. Certainly the Franks can be said to have been acting on a state policy, but any Saxon who converted was no longer a target. Jews and Gypsies could not stop being Jews and Gypsies, and could not stop being the targets of the NSDAP.
The Cathars were slaughtered because of their "heresy." They could escape that fate by recanting the allegedly heretical belief. Jews and Gypsies in the 1940s could not recant being Jews and Gypsies.
The question was about "the holocaust," which, even though there have been many holocausts in history, has come to refer to the actions of the NSDAP in the 1940s. Literary Poland, before wandering off into a cloud cuckoo land of telecommunications, made it clear that that was the event to which he referred. Therefore, the question is whether or not there were ever an event in history similar to
the holocaust. I have said that no, there has not been. I might be willing to modify that to the extent of returning to an earlier remark of mine about how similar elephants and mice are.