prevent posting to Wordpress

functions.php

add_filter( 'wp_insert_post_data', 'post_publish_filter_wpse_82356' );
function post_publish_filter_wpse_82356( $data ) {
    // view/manipulate $data
    // we still need to be able to post pages and products so just kill off attempted posts
    if ('publish' == $data['post_status'] && 'post' == $data['post_type']) {
        $msg = '<pre>' . var_export($data, true) . '</pre>';
        wp_die($msg);
    }
    return $data;
}