As for edits. Algorithm::Diff could be used, or every version could be saved and appear as links. Editing info is not always a problem and without a preview it is practically necessary. (Consider noticing broken html tags.) What tends to cause problems is when someone points out a mistake, the mistake is edited out without acknowledgement, and then the person who pointed it out gets upset that they have been made to look like they are making stuff up...
As for deleted threads, deletes are quite common. Usually the reason is a duplicated post. Deletes that cause controversy are quite rare. The last time one caused an issue that I know about was a few months ago.
Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
Want more info? How to link
or How to display code and escape characters
are good places to start.