Because you are still performing a legitimate edit - It doesn't matter whether its your own contributions or someone else's.
Removing an answer does not count towards your editing answers mission.Answer Edits and Minor Edits count towards this mission.You can see what counts towards a particular mission by filtering your contributions to show a particular action.You can do this by clicking on "My contributions" on the blue menu and then choosing the appropriate action from the drop down menu. If you select "Answers (edited)" you will see that only changes and minor changes are recorded there.
Community contributions are earned by message boards posts, profile edits, and discussion page posts.
WikiAnswers ranks your contributions by how many questions, answers, edits and community work you contribute to the WikiAnswers community.
Removing an answer is counted as an Edit.
Yes, there is a box on the right, somewhat at the bottom where there are contributions for each section such as edits, answers etc., click on one of the names or click the big green words itself (edits, answers, organization etc.).
No, neither giving nor receiving trust points count as contributions.
It has the same disadvantages this site does - it can be edited by anyone, the accuracy of contributions and/or edits cannot be guaranteed.
Making a lot of answers, questions and useful edits is the quickest way. Those with the ability can get many times more contributions by splitting and merging.
Yes
You can use AutoWikiBrowser or PyWikipedia to run a bot script to make automatic edits, or you can use Special:Import to import imaginary edits to the wiki.
Yes - even minor edits all add up to your overall contributions total. They don't add to your trust points total though. Only other contributors can do that - if they find your work worthy of recognition.