They allow the Chinese to build satellites for them and share its access together letting the Chinese survey Indian territories. They allow the Chinese to build infrastrucures like airports in their territory which pose security threats for India. They always leverage Indian support by threatening to go pro-China. They are gradually slanting diplomatically towards China. The Sri Lankan government is highly corrupt and has held back the country's development. It has a severe human rights violation record against its citizens of Indian origin and still refuses to respect their rights. It regularly creates trouble for the Indian government with acts like the arresting of Indian fishermen and is a cause of instability to domestic politics and sabotaging of India's power projection capabilities in international relations. They don't have nukes. The U.N. resolutions against Sri Lanka's human rights violations etc. give us a justifiable cause to invade them. We'll make them pay the war reparations. We could build a canal on the northern tip to route over the present journey all around the island to reach the other side. It will help demonstrate India's willingness to project power to achieve its interests.