Trying to disable plugins doens't work

Question

I've developed a small plugin which empties the $plugin variable. And put it into the /mu-plugins folder. But it doesn't work.

What am I missing? The plugin is executed.

If I do a print_r on $plugin it contains all the name of the plugins of my Wordpress installation.

The plugin code is:

$uri = $_SERVER['REQUEST_URI'];

        if($uri == "/wp-admin/admin-ajax.php")
        {
            for($i=1; $i < count($plugins); $i++ ) 
            {
                {
                    unset( $plugins[$i] );
                }
            }   
        }

        return $plugins;

===========

This is the whole code

<?php

    class DisablePlugins {
    var $namespace = "disable-plugins";
    var $version = '1.0.0';

    /**
     * Instantiation construction
     * 
     * @uses add_filter()
     */
    function __construct() {
        // Directory path to this plugin's files
        $this->dirname = dirname( __FILE__ );
        // Rules configurations directory
        $this->rules_dirname = $this->dirname . '/' . $this->namespace . '-rules';

        $this->siteurl = get_option( 'siteurl' );
        $siteurl_http_host = parse_url( $this->siteurl );
        $this->siteurl_http_host = $siteurl_http_host['host'];

        add_filter( 'option_active_plugins', array( &$this, 'option_active_plugins' ), 1000, 1 );
    }

    /**
     * Initialization function to hook into the WordPress init action
     * 
     * Instantiates the class on a global variable and sets the class, actions
     * etc. up for use.
     */
    function instance() {
        global $DisablePlugins;

        $DisablePlugins = new DisablePlugins();
    }


    /**
     * Hook into WordPress option_$option filter
     * 
     * Get processed array of active plugins being loaded for a view to allow filtering
     * based off of a user's preferences
     */
    function option_active_plugins( $plugins ) {
        $rules = $this->load_rules();
        $uri = $_SERVER['REQUEST_URI'];

        if($uri == "/wp-admin/admin-ajax.php")
        {
            for($i=1; $i < count($plugins); $i++ ) 
            {
                {
                    unset( $plugins[$i] );
                }
            }   
        }

        return $plugins;

    }
}

// Initiate the DisablePlugins class
DisablePlugins::instance();