When I type up my answers in a text box similar to this, I am able to see what my answer will look like in a dotted rectangle right below this box, including all boldings, italics, and most especially LaTeX (which this text box does not do).
I'm sure someone has thought of this, so why would the same feature not be available for comments? 80% of the time, I make a mistake when I write LaTeX in my answers and comments, but at least in the answers I am able to catch my mistake before I post it.