The essay Wikipedia is in the real world discusses the very real consequences of Wikipedia editing. Remember: Wikipedia is among the most-read websites in the world. Regardless of how many people question Wikipedia's reliability, people go to Wikipedia for information. It is highly visible.
Compare Wikipedia to a public square. When you write on Wikipedia, you're writing so anyone can read it, so do not post things you do not want people to see. Also, whether you're writing a biography or debating on a discussion page, people on Wikipedia are real, so be civil.
Also worth noting, Wikipedia keeps a record of nearly every edit forever. That means that even though a malicious edit, personal attack or vandalism can be deleted from articles, Talk pages and user spaces, it's not hard to unearth them by browsing the record of a user's contributions.
Like with anything else, be responsible on Wikipedia.