One nation or many
The issues at stake in the DMK's withdrawal from the UPA are not just ephemeral; not just about the survival of the UPA. (It will survive in any case.) They have to do with whether India is a single nation with a single foreign policy or is she a collection of many nations some of whom have diaspora for which they care more than for the nation as such.
There is no doubt that feelings run high in Tamil Nadu about the events towards the end of the civil war in Sri Lanka. There have been human rights violations by the Sri Lankan army, but no doubt also by the Tamil Tigers. After all the Tamil Tigers were the first to use the suicide bomber, often a young man or woman. (Who, after all, killed Rajiv Gandhi?)
Even so, one may say that the way in which the Tamils as the largest minority were deprived of their rights by the Sinhala majority and its leader Solomon Bandaranaike was the initial trigger for the quarrel. The Tamils tried every way of reconciling peacefully but failed. Then in 1983 the civil war began. For 25 years the Tigers challenged Sri Lankan sovereignty to establish their own nation. The end of civil war has confirmed the status of Sri Lanka as a single country.
Would India tolerate such a rebellion on her own soil? Did India not take the Khalistan challenge seriously enough to move troops into the holiest of Sikh shrines, losing Indira Gandhi as a consequence? Has India not fought a continual war since independence in Nagaland just to establish its territorial integrity? What is the whole issue of Jammu and Kashmir about? Is it not the primary duty of any sovereign nation to defend the integrity of its territory?