I am a computer scientist from Germany. I first heard about Wikipedia around 2004 when someone encouraged fans in one of my forums to write a TV show article for an online encyclopedia. I honestly expected the project to fail and forgot about it quickly. I realized Wikipedia's usefulness for (initial) uni research during 2005, and I made my first typo-fix edits as an unregistered user some time in 2006. After reading about Wikipedia in The Long Tail in December 2006, I was tempted to donate some money to the Wikipedia Foundation. In the end, I decided that I'd rather pay with my time. I became a Wikipedia administrator in December 2008. Working life has kept me from contributing much to Wikipedia since June 2009, but I still have infrequent bursts of activity.
My edit behavior and my inclusion standard are strongly inspired by the (former) Kingdom Hearts Featured Topic, whose editors merge(d) articles that cannot become a Good Article, to help other articles achieve that status and to obviate fancruft. If time permits, I improve fiction articles in that manner or participate in meta-fiction discussions. I also like fixing disambiguation and surname pages. Most of my admin edits concern non-controversial housekeeping tasks (WP:SPEEDY) or closing not-so-controversial WP:Articles for deletion.
Why don't you improve the articles instead of merging them right away? – Besides wrongly implying that mergers are not an improvement, this question does not account for scalability. I spend roughly the same time on expanding and copyediting articles, merging, and behind-the-scenes wiki stuff. Merging bad and redundant articles takes significantly less time than writing good articles, so it is basic math that I merge more articles than I expand. My Good and Featured Articles examplify the type and extent of my article improvements and may contain merged material.
Why must someone else do the work that you don't want to do? – We are all unpaid wiki volunteers, so no-one (including you and me) is required to do work that he doesn't want to do. But given certain circumstances, the answer to this question is a logical consequence of WP:BURDEN. If someone objects to see bad and redundant content merged or removed, it becomes his responsibility to improve the article, preferably using third-party sources. I am all for giving editors sufficient time to do so, but if there is no mentionworthy improvement for weeks, months or even years, then the option of merging, removal or deletion comes to the fore again.