Why do many Tamils call for a separate homeland? Because like any group of human beings, they need at least one place on earth they can call home and where they will not be treated as second class citizens. There are many accomplished Sri Lankans who refuse to emigrate to developed countries precisely because of this; sometimes esteem needs supersede economic ones.
No person is happy being treated as a second class citizen, ESPECIALLY in his own country. The response to such treatment will always be either a civil rights movement (as in early 20th century America) or a call for a separate homeland (as in Sri Lanka).
If the Sri Lankan government and the Sinhalese public become more receptive to the idea of equal treatment, a civil rights movement will be more effective than a civil war. This will undercut the rationale for militant organizations.