My views may not be entirely correct, therefore, consider this answer for illustrative purposes only, and not as an authoritative view point on the Constitution of India or the rights/duties listed therein.To understand why the Right to Vote is a recognized right and not merely a duty under the Constitution of India, it is crucial to understand the difference between a right and aduty that we have as a citizen of India - or as a part of the democracy that is made by the people and for the people.When you have/or are endowed with a right, you can enforce that right legally in the Court of law, if or when that right is violated or infringed upon. Certain rights are recognized by the Constitution of India (that cannot be legally taken away from you). For instance: Right to Equality (Article 14 in The Constitution Of India 1949), Right to Freedom (Article 19 in The Constitution Of India 1949), Right to Life and Liberty (Article 21 in The Constitution Of India 1949) among the other important ones. These rights to some extent, are also internationally recognizable by pertinent bodies like the United Nations.