Can you explain the difference between the Famine Song and racism?

If I went along to Parkhead and started singing a song glorifying the atrocities carried out by the Nazis against the Jews in World War 2, I would quite rightly be castigated and probably locked up. Like wise if I was to sing songs glorifying the riches made by British ship owners in the 18th Century by transporting Africans into slavery or even singing the praises of the Klu Klux Klan I would be branded a racist and again probably arrested for a breach of the peace. However Ranger fans seem to think that 1 million Irish people, both Catholic and Protestant, dying in the 19th Century due to their Potato Crop failing not only funny, but something to sing about with pride. It is vile racism, pure and simple. You can`t defend it and it should be dealt with same severity that the Croats are now facing for abusing Emile Heskey the other week. Unless of course Heskey just didn`t get the joke and needs to develop a sense of humour. What do you think?