That is a fair question, given that the DMK seems to be so keen of giving up all the privileges it has at the central level. It is fair to ask if they are acting in the interest of the greater good of India and Tamil Nadu.
DMK's primary interest should be the issues of Tamil Nadu. The Tamilians of Sri Lanka are a responsibility of the Sri Lankan government. The Tamilians of Bangalore are a responsibility of the Karnataka government. The Tamilians of Mumbai are a responsibility of the Maharashtra government. By ignoring the interests of the people of Tamil Nadu, DMK is doing a great disservice at a time when it could have gained the most in the last 50 years of so.
Such a lack of focus will keep Tamil Nadu in the fringes and a repeat what happened to them before the British took over the southern regions.