a small solution; the highlighting was in my blog via javascript
function pre_esc_html($content) {
return preg_replace_callback(
'#(<pre.*?>)(.*?)(</pre>)#imsu',
create_function(
'$i',
'return $i[1].esc_html($i[2]).$i[3];'
),
$content
);
}
add_filter(
'the_content',
'pre_esc_html',
9
);