Some festival in Tamil are common like Pongal. If a festival is specific to a religion, then it should be celebrated across country IMO. But yes, Tamil New year is widely celebrated by Hindus only but only Tamilians..
Tamil new year is celebrated by Tamil hindus, ugadi by telugu and kannada Hindus and so on... Stop making Hindu festivals secular. Pongal is also a Hindu festival- it's a part of sankranti of Hindu tradition. You gross ignorance can appropriate it as secular but reality is different.