So, let's say there's a question is about handling a full transaction log.

The first reply says to detach the database, delete the log and reattach the database. The OP tries that and it works. Should that be marked as the answer? It'll sometimes do what the question asks. It'll sometimes destroy your database beyond recovery.

Take a dev question. Someone asks for a query that produces a particular output. Someone posts a solution that works, but it not guaranteed to work in all circumstances (depends on behaviour that's not consistent), however the person posting it doesn't say that (may not even know). The OP tries it in a test environment and it works. Should that be marked as the answer (given that it might not work in all cases)

Debate and discussion is one of the things we encourage here. If you want a 'marked as answer', 'top voted post' mechanism, we have stack-overflow site as well for those who prefer that mechanism http://ask.sqlservercentral.com