The following databases would be a good start for general and argumentative articles on homosexuality:
Opposing Viewpoints Resource Center: A virtual library of resources from Gale designed to aid students in the study of today's hottest social issues.
Academic Search Complete: Index, abstracts, and full text for many scholarly publications covering all academic areas of study.
Also check out the Subject Guides list for a more defined subject search (i.e. religious views on homosexuality, psychology and homosexuality, etc.) Start in the library's homepage and click on the down arrow next to Library Resources.