Doesn’t even require a lack of scruples. If you allow posters to type arbitrary HTML and don’t very carefully check it, it is entirely too easy to mess things up due to innocent mistakes. The vB codes restrict you to a subset of things that can be contained, so that if you forget to turn off bold, for instance, you’ll only bold the rest of your article.
For example, if you decided you wanted a table in your message, and you forgot to close your <TABLE> tag, you would blow the layout of most of the page, which would now have an unclosed outer <TABLE>, as the first closing tag for the board display is now closing your table.
Nevertheless, I DO think it would be a better approach for the software to simply allow a restricted subset of HTML that it is willing to police and clean up before storing the message (closing your dangling syntax, for instance), and allowing board administrators to control which tags users may have (no, you may NOT have image tags - too many people are posting enormous images). It would escape all other HTML syntax as it does now. This would mean that if you already knew HTML, you wouldn’t have to look up vB codes, and the HTML tags for a few simple embellishments are no worse for the normal user to learn than the vB codes.
Anyway, that’s not how vBulletin chooses to do it. I don’t know what they provide if you allow HTML and how carefully they screen it. Apparently not carefully enough.