Answer:
Since this is an opinion and there is no right or wrong answer (I would hope because this question seems like an argument waiting to happen) I'll give answers from both sides and I'll let you choose.
Agree: Homosexual marriage should be legalized because people should be free to marry who they choose. Denying homosexual marriage would create a second class of citizens. Also the concept of "Traditional Marriage" has changed overtime and is becoming historically inaccurate.
Disagree: Marriages should be heterosexual only, because that is the only way to genetically produce offspring. Also the Institution of Marriage has traditionally been defined as being between a man and a woman. Also children need both a mother and a father.
Explanation:
