It’s much easier to have to remember fewer rules and for things to be ok if you get some wrong, yes.
Especially for casual users of HTML.
But learning about self closing tags is an additional rule
<script /> is invalid HTML, and <img></img> is also invalid HTML. There's no way to avoid knowing HTML syntax.
Bad reasoning.
“Always close your tags” is a simpler rule (and fewer rules, depending how you count) than “Close your tags, except possibly in situations A, B, C…”.