I want to create few comments custom fields for my CPT and remove the default ones.
 
I will have just two custom fields more exactly 2 radio inputs. 

Here is my code: 

    function debate_comment_fields( $fields ) {

     if( is_singular( 'debate' ) ) {

         $fields['url'] = ''; 
        $fields['author'] = ''; 
        $fields['email'] = '';

    
        $fields['first'] = '<p class="comment-form-first"><label for="first">' . 
                         __( 'HTML5' ) . 
                         '</label>' . 
                         '<input id="first" name="category" type="radio" value="'.get_post_meta($post->ID, 'agree', true).'" /></p>';


        $fields['second'] = '<p class="comment-form-second"><label for="second">' . 
                           __( 'FLASH' ) . 
                           '</label>' .
                          '<input id="second" name="category" type="radio" value="'.get_post_meta($post->ID, 'disagree', true).'" /></p>';
        
        return $fields;


    }
    } 
    add_filter('comment_form_default_fields','debate_comment_fields');  

The problem is that on my default blog posts the url, author and email fields are removed also and I'm expecting to see them there because I've added `if( is_singular( 'debate' ) ) {`

What's wrong with my code? 
Thanks!